Motorcycle Repair: Headlamp wont turn on, 81 Honda ct110, yellow lead, ground path

Question
I have a 81 Honda ct110. I have a problem with the Headlamp not coming on. I have removed the Headlamp and connected it directly to the battery, both hi-beam, and, lo-beam work. I've got the wiring diagram for the bike, all the wires seem to be wired correctly. I am using a circuit tester to follow the circuit to the head lamp. The head lamp has a blue,white, and green wire connected to it, my question to you is, the wires leading to the head lamp switch that controls the hi & lo beam, should you get some current when touching one of the wires with the circut tester, I have the tester gounded to the engine. I am getting current after the ignition switch. PLEASE HELP !

Answer
Alan, After 1975, all the street bike headlights came ON automatically when the ignition switch was turned ON and/or the engine was running.

Your wires...
Blue=High beam
White=Low beam
Green=Ground

With switch ON and/or engine running, you should have power going to the headlight control/dimmer switch.

I found this diagram on the web, which looks pretty correct:
http://techcorrect.com.au/postie/wp-content/uploads/2009/03/12vmodelwiringdiagra...

You have power coming from the stator on the yellow lead, being controlled by the regulator and feeding the lighting switch. If you have power on the yellow wire on the dimmer switch, then the next thing to check is power to the blue and then the white wires, when you select one or the other. If you have power in and not out, then the switch contacts are dirty/burned or broken. If you have power in and out of the headlight wires and up to each lead on the bulb socket, then either there is a problem in the bulb socket or the ground path is open back to the harness or back to chassis ground.

Grounding the test light to the chassis should work, but check it using the battery positive lead for power source, then clip the ground lead around the bike to ensure you have good contact with the negative battery side via chassis grounding.

Check all ground connections on the bike, as well as loose wiring connectors in the harness connectors.

Bill Silver