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REWIRING YOUR BRITBIKE (2-WIRE ALTERNATOR) - Negative Ground

- by Pete Snidal, (C)2001
- Revised Nov, '03

Is your wiring harness a mess? Weird assortments of wires, different colours spliced to different other colours, half-dissolved electrical tape streaming in the wind? Stiff, oil-soaked, or perished insulation of indistinct colours? And where did all those wires come from, anyway? Time for a change? You can build yourself a new wiring harness for less than the price of a case of beer, and an afternoon's satisfying work.

Relax!

It is almost a law of physics that the mechanically inclined tend to melt into a morass of confusion when confronted with the need for wiring changes. It must be something to do with the fact that you can't see electricity - you can't loosen a fitting and see if any is bubbling out to check the pressure, and you can't see if it's leaking. Whatever the reason, relax! This project is guaranteed to be a painless experience for all but the most intensively electrically-challenged, and will not only solve your electrical problems, but provide you with a great deal of insight for future encounters with the world of electron flow.

When you've finished this, you'll have only 4 wires running out the rear or your gas tank, a siamesed pair running from the battery area to the taillight, with a ground wire as well, and a pair running down the frame to the stoplight switch. Up front, a pair running from coils to points, and a pair running from the alternator to the rectifier. Neat, efficient, and best of all, easy to understand.

1. Positive Or Negative Ground?

Possibly the main reason for slagging Joe Lucas, ("prince of darkness," etc.) is because of superstitions over Positive Ground systems. Joe had a point, believe it or not. It seems that using Positive for the "hot" side of a DC system results in terminal sulphation - that green stuff that grows on your battery terminals in your (non-Brit) car, for instance. Joe discovered that reversing the polarity eliminates the problem, and hence Positive Ground systems. The others, notably the Americans, didn't have this figured, and set up the convention of grounding the Negative instead, and thus the war began.

There is more than philosopy involved here. A major danger inherent in a world with both systems is uneducated misconnecting. Reverse-charging a dead battery, for instance, or otherwise getting things backwards, assuming grounding one way or another. For this reason, you want always to make it very clear which terminals are which way. The conventions are: Red Wire for Positive, Black Wire For Negative. Mark with a (+) for Positive, a (-) for Negative. And be careful! Brit fans have been known to reverse-connect American systems, too! (Don't ask!) You can wire a system either way - depending on the components - but it's best to stay with the one suceeding owners/tuners will expect.

NEGATIVE GROUND

This article applies to Negative Ground Systems only. It's too confusing, I think, to try to cover both ways in one article - if you were confusion-proof, you wouldn't need an article, so I have broken my original article up into two versions, this is the Negative Ground version.

Learning Experience 1: Build A Schematic

You should have a schematic diagram, both to aid in your primary construction, and also for reference in the future. In addition, it's an easy way to do a "dry run" on the project, before you actually change anything. So, I recommend that you read this article over from start to finish, and construct a schematic diagram of your new wiring harness as you go.

The word "schematic" means that basic symbols are used - rather than in the "pictorial" fashion, in which a close-to-photographic rendition is attempted. So, for example, a circle with an A in it can represent your ammeter, a rectangle with a (+) and a (-) your battery, etc. Furthermore, less attention need be paid to actual placement of the components' representations, although it's best to have the headlight at one end, the taillight at the other, etc.

Start by making symbols on a blank sheet of paper for all your components. The ammeter, the head and tail lights, the ignition coil(s), the horn, (if applicable), the battery, the alternator and rectifier/regulator, and the switches. Once this is done, you may continue reading the article, joining the components with lines to represent the wires you will soon be connecting for real. Indicate chassis grounds with a short line terminating in small decreasing perpendicular lines. It will help to refer to a schematic in your manual for ideas for symbology. Mark the "conductors" (lines) with colour labels, or, better still, use coloured pen or pencil.

Choosing A Rectifier

There are a number of options for a rectifier - the component which changes the Alternator's AC (Alternating Current) output to Direct Current, necessary for charging the battery.

Your choice of grounding may be determined by your choice of rectifier. The standard Lucas Rectifier provides DC (+) output through its mounting stud, hence is automatically Positive Ground. The newer Tympaniums appear to be (-) bonded to their cases, as well as providing a black negative DC output line, which precludes using them without also going to negative ground.

A. Lucas Rectifier

The Lucas Rectifier - a little 4-finned thing about 2 inches by 2 inches by 1 1/2 - may only be used with Positive Grounding. If you are going to use, or stay with, your Positive Ground rectifier, you're reading the wrong article. Click here for the article for (+) ground.

C. After-Market Rectifier/Regulators

In the case of using one of these, such as the Tympanium (TM), PowerBox (TM), Mighty-Max (TM), etc. you will be able to use any of these with in a Negative Ground system.

You should check to see if your after-market Regulator/Rectifier unit will permit Negative grounding by using your multimeter set to "ohms" or "R", and checking for continuity between the red output wire and the case of the unit. If resistance is infinite, you have a choice.

Once you've chosen and sourced your rectifier option, mount it in a position as close to the battery as possible - on the battery box, or rear fender if heat sinking is required. Heat sinking will require direct bolting to a piece of metal. If necessary, mount a piece of aluminum plate in there somewhere, about the size of a postcard.

Once all the components are mounted, it's time to begin stringing wire:

TOOLS AND MATERIALS

When you've assembled these, let's go to work:

Start by removing the fuel tank. Turn off the tap(s), undo the fittings, pull the seat up/off, and carefully work the tank up and back until you can take it away and put it somewhere safe. Remember: it's full of gasoline!

Then, remove all the old wiring. Leave (or install) all components in place, but remove all wire from the entire machine. Then begin on your all-new wiring harness. You're going to build a new harness in two stages, the first to connect the various components together, and the second, once you have all the electrical system working properly, will be to wrap the new harness with black plastic electrical tape, and to fix it to the frame with black nylon snap-ties.

Mounting the Components

First, ensure that all your components are mounted on the machine.

  • Headlight Shell - with ammeter

  • Instruments

  • Running Light (optional)

  • Zener Diode (if still used)

  • Ignition Coil(s)

  • Horn

  • Battery

  • Alternator Stator

  • Switches - Headlight,
    Stop Light, Ignition

  • Rectifier (/Regulator)

  • Stop/Taillight

Running Light

In many applications, the stock Lucas parking light was a second small bulb in the headlight reflector. This was one way to run in daylight with a light, without using much power which could otherwise be keeping your battery fully charged for nightime use. If your system output has gotten low, you may wish to pursue this alternative. If you or some DPO has gone to a sealed beam headlamp, you may want to mount a clear bullet-style truck clearance lamp under your headlamp - if there's a Zener in the way, you can mount it below the Zener.

Turn Signals

The intention of this article is to celebrate the finest thing about a motorcycle: it's basic simplicity. Since turn signals don't fit into this equation, they will be dealt with in a separate article, and we'll make a separate harness for them.

Why no turn signals? It is the feeling of this author that a major danger in motorcycling lies in anything which gives the rider a fall sense of security over being seen by other road users. Forget it! - the time you think someone has seen you and is giving way is the time you'll suddenly find yourself watching your front wheel fold into the door of some multi-wheeled conveyance or another! Turn signals are a part of this equation. A little light flashing on a motorcycle is seldom seen by other drivers, and even more seldom regarded. If you like gadgets, feel free to mount and use the things, but NEVER expect ANYONE - even another motorcyclist - to change his plans based on their feeble blinking. Personally, I don't bother with them - I'd rather not have anything divert my attention from getting around the corner unimpeded by other road users bent on my second-party suicide!

Hand signals, on the other hand (sorry!) are, I feel, more of an attempt at personal communication with other drivers, and involve a conscious attempt to make eye contact - you are saying, "Hey, buddy; I'm turning right here, so go ahead and go on through!," or "Excuse me; I'd like to cut across your path here and make a left. Okay with you?" (UK riders reverse the directions there!)

For these reasons, we'll do the wiring in two phases: first the basic system, and then, later, I'll write another article on building a turn signal system.

Step 1: The Alternator Wires

The Rectifier is the center of your charging system. It is supplied with Alternating Current by the Alternator, and converts this AC to Direct Current by means of solid-state magic. The juju is not perfect - there is some heat loss associated with the conversion, and for this reason the rectifier must be "heat-sinked" to a set of fins or to a chassis component such as the rear fender, or to just an aluminum plate.

The first step will be to provide a current path for the AC by connecting Alternator output to the rectifier with a pair of wires. Being AC, these are not polarity-specific, ie they may be hooked up either way. The factory assembly system required a "quick-connect" system for slapping the thing togther on the line, but a more reliable method for you the wiring harness builder will be to shrink-tube and solder the connecting wires directly.

Cut and strip the output wires. Leave them as long as possible, but "stagger" the cuts so that the splices can't touch, even if uninsulated. Save the "bullet" connectors - leave at least 1/4" of wire in each to facilitate de-soldering if you ever need them.

For the sake of neatness, let's use the piece of black siamesed lampcord. Cut its ends staggered, to match the alternator output wires from the primary case, slip a piece of shrink tube over each wire, and twist and solder the two conductor pairs. You MUST use Resin-Core solder for electrical work - Acid-Core soldering will soon corrode.

Then, slip the shrink tube over the splice, and heat it gently with the BIC lighter until it shrinks tightly over the splice. Route this wire up to the position of the bridge rectifier, and cut it so that you'll be able to connect the ends to the rec's AC input terminals. Do this, using crimp-on spade connectors, or soldering as necessary. Since it's AC, and therefore non-polarity-specific, it doesn't matter which wire connects to which AC input terminal. If you're using a rectifier with studs to which the wires must be soldered, be sure to heat-sink the stud with a pair of needlenose pliers (yes, you need three hands!) Use shrink tubing to insulate the studs after soldering the connection. Do not shorten them - you don't want heat from soldering to travel into the component; it can be fried. The studs may be bent for routing convenience, but support them at their base with a pair of needle-nose pliers before bending.

Your rectifier is now supplied with AC input! Now for the DC output to the system.

3-Wire Alternators

One last complicating factor: does your alternator have three output wires? If so, it's a 3-phase, and will require a 3-phase rectifier/regulator unit. See separate article

The Chassis Ground

Choose a ground point close to rectifier and battery - one of the tabs on the frame, such as the one for the old rectifier mount, for example. Be careful not to use a point on the battery box - it is most likely rubber-mounted and therefore insulated from the chassis.

Be sure to clean your chosen area down to shiny bare metal, and when connecting, be sure to use the proper colour - Black. Strip the end for about an inch. Twist this bare wire, and bend it into a loop around a 1/4-20 X 3/4 cap screw. "Tin" this loop by heating it with the soldering gun until resin-core solder will melt into the weave. Screw it to the frame lug with the cap screw, nut, and a washer - leave it loose; there are more to come.

The Rectifier Output

We will be using Negative Ground, or "earth" - meaning simply that the return path for current from the various devices to the battery is accomplished by using the chassis as a conductor. The battery (-) terminal - Black wire - is "grounded," or "earthed" - connected directly to the chassis (although fused). The battery (+) terminal - Red wire - is the "hot" one (relative to the chassis) and is the one run through switches and conductors and run to the various devices - ignition, lights, horn, etc. The point is almost moot, since the best thing to do is to use a second wire for the return path, a plan which we'll use in most cases here. But we'll "ground" one side of the circuit as well, just to avoid confusion.

Connecting The Rectifier DC Outputs

The Rectifier Negative Output

The Rectifier Positive Output

Now for the "hot" rectifier output.

The Battery "Hot" Wire

Now to connect the battery "hot" wire - the one which will carry charging current from the rectifier through the ammeter back to charge the battery.

The Light Switch

Now is the time to figure out your headlight switch. If you have a factory wiring diagram utilizing the switch you have, you can just identify the terminals (usually by number) and note where they connect on the diagram - the "in" terminal, the taillight, the dip switch, the park light(s), etc. If not, it's time for an exercise in logic.

There will be an initially bewildering array of terminal possiblities, but they work out once you find the INPUT, or "hot" terminal. You'll want to draw a picture of the back of your switch on a piece of paper, showing the terminals, with room to write in an identifier for each.

1. Find the "Hot" - Input - Terminal

To test your switch, a number of methods could be used. Best of all is a continuity tester, such as a multimeter set in the "ohms" position. Start by looking for the "0" position - the one in which none of the terminals shows any connection to any another. This may be at one end of the movement spectrum, or in the middle, such as park-off-head.

Then move the switch to the "1" position - the first click. Look for connections between pairs of terminals - you need to find the park and taillight terminals, both of which will be connected to the "hot" terminal, but not to each other, and of course the "hot" terminal itself. It's the one that will show as connected to BOTH of the other two in the "1" switch position. One of these is for the park, or running light, the other for the taillight. (The reason they don't connect together in the "1" position is because, if they did, the Park light would be fed back from the taillight wire in the "2" position, and to the headlight in the "1" spot.)

Once you've identified the "hot" terminal, you've solved most of your problems with the light switch. Mark it, and the other two which light up in the "1" position. But which one is which?

Now, move the switch to the "2" position. In this position, the "in" connector will power the taillight and headlight terminals, but not the one for the park light. That is, one of the two connected to it in the "1" position will also be powered in the "2" position. This is the taillight terminal. The other, the one powered in "1" but not in "2," will be the park light terminal. The one powered in "2" which is not the taillight terminal is the headlight terminal. Logical, huh? If you're still confused after thinking this over for awhile, maybe a chart will help:

The taillight terminal is the one which is connected to the "hot" terminal in BOTH positions "1" and "2." The Park, or running light terminal is the one which connects in postion "1," but NOT in "2."
Connection to Input Terminal
TerminalPos 0Pos 1Pos 2
Park LiteNOYesNo
Head LiteNONoYes
Tail LiteNOYesYes
 This leaves only the Headlight terminal. It is the one which is connected to the "hot" terminal ONLY on position "2," but not on "1." This is the terminal from which you will feed the "hot" wire to the dip switch.

System Outputs

Once you've got your light switch diagrammed, connecting the switch inputs is simple. You will connect them in a "daisy chain," "piggy-backing" each input wire from switch to switch as you did from the ammeter terminal. All system outputs will be from the same ammeter terminal as is connected to the rectifier output. These will be the feeds to the the light switch, the ignition switch, the horn, and the turn signal flasher, if turn signals are going to be fitted.

The first connection will be with the wire you "piggy-backed" to the ammeter connection. This white wire goes to the input of your Light switch.

The Light Switch

Cut this wire from the ammeter/rectifier output to a suitable length at the light switch. Strip the end, and that of another piece of white wire. You may use the thinner #16 if you like, since the major draw - that of the Lights - terminates at this connection. Crimp both of these ends into a suitable connector (ring or spade) and connect to the ignition switch input. You have now made a second "piggy-back" connection, this time for the next switch in line, the ignition switch.

Do the same thing from the ignition switch to the horn - connect this "hot" wire to either horn terminal. Your input connections to the light, ignition, and horn are now complete.

Outputs - from the switches

Ignition Switch - Yes Or No?

You can use your light switch as the ignition switch as well. Since the taillight terminal is fed "hot" in both switch positions, it can be used to feed the ignition at the same time. You have no key this way, but since motorcycles are ridiculously easy to hot-wire, it hardly reduces the stealability to eliminate the key switch - you need to lock your machine securely to a lamp pole or something solid, or at least use a fork lock to ensure that it will take longer than a minute or two to steal it, anyway. So a key switch really just contributes to a false sense of securitity. Besides, who's to know that turning on your running/park or headlight also switches on your ignition?

If you choose this option, "piggy-back" a WHITE ignition wire in with your GREEN tail light wire and connect the pair to your taillight terminal on the light switch. At this time, be sure also to "piggy back" connections with the taillight green wire to the instrument lamps - speedometer and/or tachometer. The white ignition wire goes to the coil's "hot" terminal - marked (+). In the case of twins, "piggy-back" the white wire from the first coil hot terminal to that of the second coil as well.

If you wish to retain the ignition switch, connect the ignition switch input to the "piggy-back" wire from the light switch input. Be sure to continue the "daisy-chain" with a piggyback connection for the next load in line - the horn.

In either event, the last load in the daisy chain of "piggy-backed" connections is the horn. Connect the end of this wire to either of the horn terminals.

Ignition Switch Output

If you have chosen to retain a separate ignition switch, the output of this switch goes to the coil(s) as described above.

Coil-to-Contact Breaker Connections

The other coil terminal in either of the above cases must be connected to the contact breaker moving (non-grounded) point. In the case of twins, there will be a point connection for each coil. These are cylinder-specific; the point set which opens for any given cylinder on the top of the compression stroke (both valves closed) is the one for that cylinder; its coil high-tension lead must connect from the proper coil to its spark plug.

Electronic Ignition Systems

In the case of after-market ignition systems, follow the wiring instructions supplied with the system. There will basically be a Black Negative Connection, (ground this), a Red Positive Connection (connect to switch output), and connect the two wires to the reluctor which replaced the points.

Light Switch Outputs

The Terminal which goes "hot" with the switch in the No. 2 position is for the headlight switch. Connect this terminal to the input terminal of the dip switch. The input terminal is the one which is connected to one of the others in only one position, and to the other in only the other position. The two remaining lines are for high and low beam of the headlamp.

The Headlamp

The Headlamp has 3 connections: High Beam, Low Beam, and Ground. Be sure first to connect the ground to the ground point inside the headlamp. Then, using a jumper wire from the battery "hot" terminal, with a fuse TEMPORARILY in the battery ground fuse, determine which line is which. A bit of experimentation will reveal which line needs to go to which between the two dip switch outputs and the two headlamp inputs. Be sure to connect the high beam indicator to the proper line as well.

Park/Running Light

The terminal which goes "hot" in Position 1 of the light switch (but not in position 2) is the park, or running light terminal. Connect this to the park or running light(s).

The Horn

In almost all cases, the horn is not internally grounded; ie, it depends on one terminal being grounded by the handlebar switch to be activated. The other terminal is always "hot" with ignition on. Thus the "daisy chain" of output wires from the ignition switch ends at the horn input terminal. Horns are seldom polarity-specific; energize either one with the ignition circuit, ground either one through the switch, and you have a horn.

STOPLIGHT CIRCUIT - 2 wires

Now, take the siamesed lamp cord wire, and connect one of each wire to each connector on your stoplight switch. You may have to salvage a pair of "bullet" connectors from your old wiring - they solder on and off. To remove a bullet connector, first wipe it clean, then heat the tip with the soldering gun until it may be pulled off with a pair of needlenose pliers. Be careful not to collapse the bullet connector!

Once it's free, shake it immediately at the floor to expel the still-liquid (if you're quick!) solder. Installation is the reverse - be sure not to apply too much solder; just a little at the tip should be enough.

Now, run the lampcord up a frame member past the Rectifier to the taillight along the top of the rear fender - this is just to get the length. Cut it with a handspan to spare.

Lampcord usually has a "tracer" to distinguish between the two conductors. Identify the tracer - usually a grey line on one conductor. Then, at a point close to the rectifier fuse ouput, cut ONE of the two conductors - let's say the one with the trace - at a suitable point, and strip and twist the lower (switch) end to the rectifier fuse output wire. Solder and shrink-tube the joint. This is the "hot" feed to your stoplight switch.

The other end of the cut conductor will feed the taillight. You may now pass one end of a suitable length of GREEN #16 wire through the headlight bucket from the front, and along the lower frame tube to the location of the ammeter fuse and remaining unconnected end of the conductor you just broke. Strip-solder-shrink the green wire to the open end of the cut conductor. This is your taillight feed.

Most motorcycles have some sort of channel under the rear fender for the tail/stop light wires. Use this channel, if it exists, to route the siamese cord from fuse location to that of the taillight. Include also a third ground wire - this should be red for (+) ground systems, and black for (-).

Fit the ground wire to the taillight body, using a ring connector or strip-twist-bend-tin a ring. Fit the ring under one of the taillight mounting bolts. Beware of rubber mounting insulating the connection! Connect the front end of the ground wire to the chassis ground point. If you are in doubt about which taillight wire is which, TEMPORARILY install the battery ground fuse, and use a temporary jumper wire from the "hot" battery terminal to each of the the two wires at the taillight - connect the taillight ground first! The brighter of the two possibilities is the Stop Light - the unbroken conductor of the siamese pair. Strip, shrink, and solder the two taillight wires to the siamese feed lines.

Testing The System

With all these connections made, it's time to test the system. Install the fuses in the fuseholders, and do the engine-off test first. Turn on and check the Park lights, and the headlight, (both beams) in turn. Check that all lights are working. If not, check with a circuit tester to ensure that power is available at the unit in question (ie, is the bulb burnt out, or is there a problem with the switch or wire?) Check also the horn, and finally, check the ignition by removing the spark plug(s) and, with the spark plug connected and lying on the top cylinder head fin, roll the engine over with the kickstarter, ignition on, and check that you have spark. Trouble shooting is much easier with all the wires exposed, not yet taped into a loom.

When loads are switched on, the ammeter should move to the Minus side, the left, or into the red area. If it moves in the opposite direction, remove the battery ground fuse and reverse the connections at the ammeter. Replace the fuse.

Once the system checks out, carefully tape the wires into one loom, starting at the front just inside the headlight. Do not use too much tape, ie just a small amount of overlap on each turn. When the loom is done, fix it to the frame at strategic points with black nylon snap-ties. Remove the battery ground fuse, and reinstall the fuel tank - be sure to tighten the fuel lines securely. Then replace the ground fuse - you removed it to prevent any possibility of short making sparks as you installed the fuel tank.

Start the machine, and ensure that the ammeter moves as you increase the rpm above idle. It should move to the right, in the direction of the Plus sign, or into the green area, as you increase rpm. If it doesn't, check the charging system. Once the system checks out, you can put away your tools and congratulate yourself on your new-found electrical expertise. You've finished the job!