Need help troubleshooting why headlight has no power

[mrhammer2u]

The bulbs is fine, problem is I'm getting no power to it. Me and a friend have scratched our heads long enough,...need help..lol. Any and all ideas are welcome. Fuse is fine and line does not seem to be cut. It worked in the fall when I put her away.

[mack]

diode

There is a diode in the harness before it gets to the bucket. They are usually marked with white tape. Mine was on the tank side almost at the yoke. You could start there. I can't remember off hand but someone here knows what the compatable car part number was for a replacement.

[bikerphil]

If it is a 79, there is no diode in the harness, it is contained in the headlight relay. You can try bypassing the relay (safe) by unplugging it's 4 wire connector and jumping red/yel and blu/blk wires in the harness plug. Headlight should hopefully come on with the key in the on position.

[skids]

And if that doesn't work, you might try cleaning-up the connector from the alternator. It is behind the fuse panel plate. One of the wires (looks like 4 whites but one may be pale yellow?) will power the "lighting unit" which also is a solenoid to turn the light on (relay). That connector clip is a common problem with these bikes. I had a tachometer failure on one of my xs11s when the headlight also failed to work.

[crazy steve]

And if that doesn't work, you might try cleaning-up the connector from the alternator. It is behind the fuse panel plate. One of the wires (looks like 4 whites but one may be pale yellow?) will power the "lighting unit" which also is a solenoid to turn the light on (relay). That connector clip is a common problem with these bikes. I had a tachometer failure on one of my xs11s when the headlight also failed to work.

Yep, the yellow wire powers the relay on the '78-79 bikes. This wire is unused on the later bikes, ending at the field winding plug.

[skids]

This wire is unused on the later bikes, ending at the field winding plug.

What is that plug?

[crazy steve]

The plug from the alternator that plugs into the harness behind the fuse panel and is noted for melting....