Motorcycle Repair: Honda Trail 55 Wiring

Question
Bill, I have a 1963 Trail 55 (Chrome Model) that I'm trying
to wire up and am using the c100 diagram. I'm trying to figure
which wire is hot to the switch? If you follow the diagram up
from the battery there appears to be no hot wire?

Thanks for your help! JG

Answer
Jeff, I generally use the diagrams on http://oldmanhonda.com/MC/WiringDiagrams/MCwiring.php#class, however the wiring diagram for the C100 is of rather poor quality and is missing some details concerning the brake light switch and wiring to that filament.

I pulled up http://www.cmsnl.com/classic-honda-fansite/honda_wiring_diagrams/C110-C110D.jpg instead which is more complete and a little bit clearer as far as wiring colors and details. The Sport Cub is pretty much the same as the regular "Cub" model, electrically. The Cub drawing was done about 1958 and the Sport Cub updates in 1961-62, so they are improved.

It is easy to try to apply "acquired knowledge" to a given situation and then become stymied when it doesn't seem to apply, isn't it?  In this case the ignition switch is being used more to switch the ground side of the circuits, rather than to switch the positive side of the power, which is what we are all used to, these days.

Honda's Cubs were designed in the late 1950s and they just used some different thinking to where the switch should be, electrically, in the circuit. Because the ignition power is being generated from the self-generating magneto, not the battery, the ignition switch puts ground on the ignition to turn it off, when it is placed in OFF position. If you disconnect the ignition switch from the chassis, you cannot turn the engine OFF electrically.

The switch functions to apply ground on the battery circuits in order to complete the circuit. A DC voltage circuit can be switched ON or OFF from anywhere in the circuit. In this case, the DC power which runs the horn, neutral light and brake light is completed when the switch is turned ON and the circuit completed internally to the grounded switch base.

You just have to follow the wiring diagram's color coding, just as it is and the rest will take care of itself. As long as all the wiring colors are correct/original and you connect all of the wiring up as coded, the wiring should work as designed. Follow the wiring diagram to ensure that the ground paths are provided for, as drawn, too. With a chromed frame model, vs. a painted or powdercoated chassis, there shouldn't be any issues with grounding the circuit correctly.

I hope this answers your question sufficiently. It is a little bit confusing when you apply known logic to the circuit diagram and what is commonly seen in Honda wiring diagrams and switch functions since then. It doesn't "make sense" but it DOES work quite well.

Bill Silver