Electrical gremlins... headlight relay

Oh my gosh, I love this forum!! Thanks to Beekman for the photo of the jumper. My headlight relay is in the same place, behind the left side cover. Headlights work with the jumper, didn't work with the factory (metal case with 3H5 stamperd on it) relay. Carefully opened the relay, tried contact cleaner spray, which didn't work, and ended up running a narrow folded strip of 300 or 600 grit wet/dry sandpaper between the contacts a few times. It didn't work until I ran the sandpaper through while applying pressure directly to the contacts with a wooden shim. Now all is right, and light, with the world.

My next mod will be to replace the halogen bulbs in the headlight and driving light with LEDs to reduce the electrical load on the system. More research is necessary.

1982 XJ750RH, my second Seca 750!

 

My Headlight relay is bad. No Headlight, no lights on the tach/speedo.
Unless the engine needs to be running for headlight to work?
I put in a new fuse box and I'm getting voltage to the relay connector, but no click on the relay.
The relay for the tail lights work and turn signals work fine.

3H5 Relay and it is under the side panel like above.
1983 XJ650 Maxim

 

answering my own question, Headlight relay needs enough voltage that is only available when the alternator is running.
I am rebuilding carbs this week so looking for a way to test the relay and lights. I guess one way would be to hook up the battery to a higher power source like jumper cables to my car?
I'm going to make sure my battery is fully charged though. Don't think my charger will get the voltage high enough to match the alternator.

 

It's not a matter of voltage amplitude, it's about applying the voltage to the relay pin that goes to the alternator. I suspect the pull in voltage for the relay is less than 8V. Once it pulls in it will latch, which is why the headlight stays on when the bike stalls or sometimes when trying to start and not quite there but the headlight comes on and stays on unless you cycle the ignition key

 

ahh, thanks Rooster!, that diagram explains everything. So if I want to test the headlights and at least the latching part of the relay w/o starting the bike, I just tap short the R/Y and L/B connections or tap short the R/Y and W connection?

(still waiting for parts to rebuild carb)