Head lights doing weird things HELP

have 1 90 firefly convert, my left headlight is weird.....I have changed the headlgith twice. Each time the left one is lit ver very dimmly, and when I put the hightbeams on it the left cuts out totally. Fuses are fine. ??Anybody help. Is it the harness that attaches into the back of the light?

Check the wiring runnning to it. There might be a short in the wire.

Get a Volt Ohm Meter (multimeter), disconnect the light plug, turn on the lights and check the voltage at the positive wire on the plug with the negative probe grounded to the chassis or the negative terminal on the battery. If you don't have 12 volts at the plug, back track through the connections untill you do. If you have 12 volts at the plug, turn off the lights and check the resistance on the negative wire at the plug with the negative probe still grounded to the chassis or negative post, it should be 0 or very close to it. If it isn't, back track through the connections untill it is. Your problem will be between the 2 connections where your reading changed. The most likely location of the problem is going to be the light switch or the negative wire since it is affecting both the low beam circuit and the high beam circuit.

Good Luck!!