ok dude, i don't know what a PC50K1 is, but i know this: If you have only one or two wires coming from the engine, then good luck.
but if you have like 5 or 6 wires, disconnect the horn and ground the wire, then reconnect all the wires in the headlight (and if they go to the speedo light, make sure those are solid.) once your headlight works, then put your horn back into the rig. This is just to get one thing working at a time. Doing all the electrics at once is a pain in the ass.
but its probably just what harrold said, a bad ground