79 xs 650

[XSLeo]

You might want to check the alternator output. If it has no output the headlight won't light up.
When the engine starts, the alternator starts making power. When the output voltage reaches about 4.5 volts on the yellow wire to the safety relay, the relay trips and turns off power to the starter relay so the starter stops working. It also turns on power to the headlight. So if the alternator isn't working, you get no voltage on the yellow wire, so no headlight.
With the bike running, check the battery voltage. At idle around 12.5 to 13.5 is ok. As you rev it up a bit the battery voltage should rise up to and never exceed 14.5 volts.
Also on your fuse box the clips that hold the fuses where fine 30 years ago, but are pretty much crap now. A good thing to do is remove the stock fuse box and replace with inline blade type fuse holders. This can help fix a multitude of electrical problems.
Leo

 

[stemy]

where is the fuse box at? all i found was a fuse that was coming off my starter relay.

 

[XSLeo]

Should be a box that holds four fuses under the seat.
Even on the earlier models that had just one fuse it wasn't on the starter relay. It was between the battery and key switch.
Sounds like some one may have done some creative wiring.
Leo

 

[5twins]

Well, that one fuse on the Standard is actually by or next to the starter relay. It doesn't run off it but is situated right next to it .....

The Standard models have only the one fuse. That fuse box was a feature on the Specials.

 

[XSLeo]

Yes, one fuse on the early standards. In late 78 they went to the four fuse box on all models.
Leo

 

[stemy]

i have a fuse by the relay but i can't find any other fuses, unless i over looking them..

 

[stemy]

well i think my battery is junk, it seems like its not holding a charge.

 

[XSLeo]

If you only find one fuse, and it should have four, it sounds like a po has done some rewiring.
I think I would start at the battery and trace the red wire to see just where your power flows.
Leo

 

[stemy]

i unhooked my safety relay and pluged it back it and now im not getting power anywhere.. i'm getting irrated with this..

 

[Kingwj]

The standards have only one fuse. And yours is exactly right. If you have no power anywhere check the fuse.

 

[Kingwj]

Yes, one fuse on the early standards. In late 78 they went to the four fuse box on all models.
Leo

Ummmmm, no they didn't.

 

[XSLeo]

Then when did they? In all the diagrams I've looked at 78 was the year they started using the four fuse box.
Leo

 

[Kingwj]

I believe the standards went to their grave with a single fuse, my '79 is the same single fuse next to the starter relay and it is stone stock as from the factory original. The wiring diagrams don't reflect the real world.

 

[hmusket]

FWIW, looked at the wiring diagrams in my Clymers, there's an early and late version for '78. Early version, one fuse, covers SN 2F0-000101 - 2F0-006501. Late version, 4 Fuses, after 2F0-006501. Pages 6 and 7, of the wiring diagrams.

 

[stemy]

My fuse is good. Is there a way to check the saftey relay? Or is there a way I can bypass all this stuff and wire up a switch for my headlight?

 

[Kingwj]

FWIW, looked at the wiring diagrams in my Clymers, there's an early and late version for '78. Early version, one fuse, covers SN 2F0-000101 - 2F0-006501. Late version, 4 Fuses, after 2F0-006501. Pages 6 and 7, of the wiring diagrams.

I guess they changed back to a single fuse for 1979. 'Don't believe everything you read' seems to be relevant in this case.