I used Radio Shack # 274-1583 coaxial DC power jack with switch for 5.5 mm OD, 2.5mm ID plug.
The R.S. jack has a pin label diagram on back of card:
Shell - hook to R70 Red wire
Center pin - hook to R70 Black wire
Normally closed switch contact - hook to R70 Yellow wire
I had to extend those wires after I clipped them off the DC power connector hidden loose inside the radio. That makes them much easier to attach. The thin purple wire is for memory retention. I tucked it back inside the radio after clipping it off the original DC connector.
Wire the plug for NEGATIVE center pin. The case of the DC jack is positive, which is why I had to isolate it from the radio's case. I used a piece of thin fiber-board, (masonite?), and widened the area where the stock DC power connector is supposed to go.
The hard part was mechanically mounting the jack. I removed the power supply to do it. The fiber-board mounts inside the power-supply's case. I had to custom-shape the fiber board to mount using the existing holes - 2 for the original DC power connector slot cover, and 1 of the adjacent AC power jack bolts. I had to trim a small piece of metal out of the power supply case, and widen the area on the radio's rear panel for the DC power jack to stick through.
Make sure your DC power-cord has an in-line fuse. 1 Amp fast-blow. Hook cable to battery first. The R70 has an input filter cap ahead of the power switch. It will likely draw a spark at the battery if you hook up battery end of cable last.
Larry Russell .... in Flushing, Michigan