REWIRING YOUR BRITBIKE (2-WIRE ALTERNATOR) - Positive 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
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
Choosing A Rectifier
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 if necessary.
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.
A. Lucas Rectifier
The Lucas Rectifier - a little 4-finned thing about 2 inches by 2 inches
by 1 1/2 - is surprisingly robust. Many still survive after 30+ years.
They are old-new-tech, however, utilizing the earlier Selenium Diodes
rather than the more modern Silicon. For this reason, or because yours
no longer functions, you may wish to switch to silicon-technology -
discussed later. If yours is still working, though, you may wish just
to leave it in place. You'll need a functioning Zener voltage regulator
as well - the Stock Lucas one may well still be functioning on your
The Lucas Rectifier assumes positive ground, the DC (+) output fed
directly to the chassis through the mounting bolt. It doesn't hurt to
crimp a ring onto a piece of red wire and connect the other end directly
to the battery (+) terminal. For belts-AND-suspenders protection, you
should choose to install a fuse in the line between the (-) "hot" spade
connector on its way to the ammeter with a black wire.
B. Generic Bridge Rectifier
One of these may be used to replace the stock Lucas Selenium Rectifier -
reasons discussed above. As well as better efficiency, these have the
advantages of economy - they cost less than $10.00 - and local
availabiltiy - they can be had from any electronics supply house, or
often even your friendly local Radio Shack (TM). You'll need
one with a rating of minimum 20VDC and 15 Amps. They come with spade
or pin connections. If the only kind you can get is pin, be sure to
"heat sink" the pins with a pair of needlenose pliers when soldering the
connection wires to the pins. Shrink tubing can be used for insulation.
The rectifier itself must also be "heat sinked" to a piece of aluminum
plate or some part of the machine, such as the battery box or rear
fender. It's a little extra trouble, but the savings are significant.
The Zener regulator will also be required with this unit.
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 may (or may not!) have the choice of
which DC output to use as ground. Although I have previously found that
Tympaniums, for instance, could be used either way, I just bought two
Negative Output lines are tied electrically to the case - meaning using
Negative Ground or insulating the heat sink from the frame, leaving it
"hot" to the chassis. I elected to go with Negative Grounding - Battery
(-) being grounded, and (+) being fed by the ammeter. Red wire from
Tympanium output to the ammeter (+) terminal. In this case, it's good
practice also to fuse the hot output line, whether (+) or (-). Thus,
shamefully, I have changed my Triumph to Negative Ground! (This also
meant changing my coil connections, and reversing my ammeter lines.)
You can check to see if your after-market Regulator/Rectifier unit will
permit a choice of grounding by using your multimeter set to "ohms" or
"R", and checking for continuity between the black output wire and the
case of the unit. If resistance is infinite, you have a choice, and
should stay with the stock grounding for your machine. If Resistance is
Zero, you will have to look for another unit, or go to Negative Ground,
no longer drinking upstream from the herd. If you do elect to convert,
be sure to remind yourself and any further mechanics that it's been
changed. A label or two, carefully using RED wire for positive, ie to
the ammeter connection, and a BLACK wire (and fuse holder!) to the
ground connection, should clear up the battery connecting for all but
the least observant. You should definitely fuse the battery ground, and
the rectifier (+) output as well - using a RED fuse holder in the RED
wire to the Ammeter (+) terminal. The DC from that little battery is
plenty enough to light up wires in the case of misconnection (as well as
fry your Reg/Rect.) Leave the fuse out of the holder for the time being.
If there is no continuity between the case and the Black (-) DC output,
you will have a choice as to ground - if Positive Ground is the stock
way, stay with it; it's best anyway. (No terminal sulphation.) In this
case, feed the Ammeter (-) terminal with a black wire from the R/R black
output, - shrink and solder - and ground the Red DC output. Once again,
you should fuse the "hot" output line. The fuse will protect the Rectifier
against any short in the charging system, reverse-connection of the
battery, or any other possible threats to the longevity of it or the
alternator. The Zener is not required with these units.
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:
This article applies to Positive 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 Positive Ground
version - for originally Lucas British-built systems. If your system is
Negative Ground, or if you're going to be using an aftermarket
rectifier/regulator unit which is case-bonded to the Negative Output, go
to the negative ground article.)
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
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.
TOOLS AND MATERIALS
A selection of ring and spade terminal connectors - you will need an
extra-large one for the Zener Diode, if you're going to use it. Have a
look and see.
Two 10Amp fuse holders, and some spare fuses. Get a black
fuseholder, and a red one, if possible.
A pair of side cutters
a connector crimper/wire stripper
selection of #14 and #16 automotive stranded wire in various colors -
minimum black and red - but green, blue and white will help to make
things less confusing later.
6 foot/fathom/armspan/2 metre piece of black siamese lamp cord
the usual screwdrivers, wrenches, etc.
A soldering gun or iron, with resin-core (electrical) solder
A selection of shrink tubing, a pair of scissors for cutting,
and a BIC lighter for heating/shrinking
A selection of nylon snap-ties. Black, if that's the colour of
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
Running Light (optional)
Zener Diode (if still used)
Switches - Headlight, Stop Light, Ignition
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.
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
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
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 - Red.
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
Most British Motorcycles are Positive 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 - red wire - is
"grounded," or "earthed" - connected directly to the chassis. The
battery (-) terminal 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 Positive Output
1. First, identify the Rectifier's Positive DC output - a red wire, a terminal
marked (+), or the case/body itself. If your rectifier is still the
standard Lucas, your only postitive DC output will be the mounting stud
itself. Mount this to a freshly-cleaned part of the frame (such as the
stock mounting tab.) This will also be the battery ground point. Mount
two red #14 ground wires to the other side of the connection - under the
nut - you can use a ring terminal with both wires crimped into it, or
use the strip, twist, bend, and solder method.
2. Connect one of these red wires to to your battery (+) terminal
through a fuse. This fuse will protect your system from any damage from
battery power should a short occur somewhere.
second red #14 wire goes inside the headlight. Drill a bonding screw
hole in an unobtrusive spot at the rear bottom of the headlight, and
mount a 10-32 screw and nut into this hole. Run the red wire along the
lower frame member - above the engine - to the inside of the headlight
shell. As it passes the coil bracket, strip the insulation for an inch
or so, loosen a coil bracket bolt, and pass a loop around the bolt,
under the washer. Then cut the wire to length, strip, twist, bend, and
tin, and fix it under the washer to the headlight bonding screw. Leave
it loose - there are more to come.
The Rectifier Negative Output
Now for the "hot" rectifier output.
1. Pass one end of a piece of BLACK #14 wire through the front of
the headlamp, around the fork neck, and down the lower frame tube to the
rectifier. Fix a fuse holder to the end of this wire, using shrink
tubing and solder for the splice.
2. Fix the remaining end of the fuse holder to the rectifier "hot" (-)
3. Then cut the wire at the ammeter end to a suitable length
to connect to the ammeter (leave a little slack).
4. Now, strip one end of a piece of WHITE #14 wire long enough to
reach the input terminal of the light switch. Twist the end of this to the
end of the rectifier output wire, and crimp them both into a ring connector.
Bolt this ring connector to the (-) ammeter terminal. You have now connected
your ammeter input, and "piggy-backed" a second wire to feed your ignition
The Zener Terminal
- The following applies only to Systems, using either the stock Lucas
Rectifier, or an electronics generic Bridge Rectifier, and thus still
requiring a separate Voltage regulator. If using an after-marked
Regulator/Rectifier unit, such as the Tympanium (TM), Boyer Powerbox
(TM), or Mighty Max (TM) - the Zener Regulator will not be required.
If so, disregard all this Zener stuff. The Zener
and bracket may be left in place, however, for authenticity's sake.
If you still have the Zener Voltage Regulator,
1. First ensure that the Zener case is securely grounded to the
chassis. Remove the Zener from its bracket, and clean up the metal
interface with sandpaper.
2. Using Red wire and appropriately-sized spade terminals,
connect the Zener and its bracket to the headlight chassis ground
screw - the one with the red wire from the rectifier fuse.
3. Now, connect the "hot" (-) Zener terminal to the ammeter
(-) terminal - the same one as the wire from the rectifier. Use Black
#14 wire. (You'll need the extra-large spade connector here. If you
can't find one, you may elect to use a short piece of your old wiring
harness, retaining this old large connector.)