I’m going to replace the main wiring harness. This requires removing a number of connections inside the headlight shell, pulling the old harness out of the headlight shell and then installing the new harness and connecting the wires to the proper terminals on the wiring block, the headlight relay and the turn signal relay. You do not have to remove the connections from the left and right handlebar switches to replace the main wiring harness.
Bur, since I am converting this 1983 R100RS into an RT configuration and the RT handlebars are much longer than the RS bars, the stock RS handlebar switch wires are too short; 230 mm (9 inches) vs.the RT switch’s 520 mm (20 inches). However, someone replaced the left handlebar switch with an RT length switch, so that’s fortunate. But the right handlebar switch, that was also replaced at some point, has shorter 380 mm (about 15 inches) wires; they are longer than RS wires, but still too short. Since BMW does not sell the RT switches anymore, I will lengthen the wires in the right handlebar switch cable.
Here is how I did that work.
And here are videos summarizing the procedure.
VIDEO: 1983 BMW R100RS Replace Main Wiring Harness
VIDEO: 1983 BMW R100RS Lengthen Handlebar Switch Wires
Here is the new main wiring harness I got from Euro MotoElectrics. BMW not longer makes this harness.
Here is the final product.