Headlight will not turn on

[Junkwire]

I have been scouring the internet for hours trying to figure this one out. So, if I understand you guys correctly, On my (wife's) '81 XS650 Special II, I need the RLU (Ridiculous Laughable Unnecessary) bypassed (Blue/black to Blue/yellow on the harness), there's a light relay that has to engage, and I need input from the stator (motor running, or at least started) in order for the headlight to turn on?

 

[gggGary]

Yup that's the story.
A separate lead from the stator (yellow wire) provides about 6 volts AC to the relay which then latches and stays on until the next ignition switch cycle, even if the charging system quits. Note there is also a headlight fuse in the notoriously fragile fuse box.
Here's the lighting circuit separated out.

 

[Jim]

Yes, there's a yellow wire from the stator that sends 6vac to the light relay, so you need to check that it's charging.... about 14-14.5v at the battery when you rev the engine.
Without look it up, yes those colors sound right for bypassing the RLU.
Not to be a smartass.... but make sure the headlight isn't blown too.

Oh... and welcome to the forum!

 

[Junkwire]

Thanks for the 'Welcome.'
I used to be an electronics tech, so no offense taken. It's the simple things that trip us all up.
The headlamp is good, it was tested on the Subaru battery.
There are a slew of lights not working, the clock lights don't work. Just the stuff attached to that yellow wire all over the diagram.
And the rear brake light switch doesn't work. And the flasher relay is bad. But I bought the thing for $250, and she really wants to run.
Thanks for the conformation, now I know where to look.

 

[5twins]

The motor doesn't actually have to be started and running. Just sustained cranking, enough to get the alternator generating some output, is enough to trigger the relay and turn the headlight on.

 

[gggGary]

The motor doesn't actually have to be started and running. Just sustained cranking, enough to get the alternator generating some output, is enough to trigger the relay and turn the headlight on.

With a healthy system, a good kick on the lever will do it.