Headlight failure

spills · Nov 22, 2017

Hey all,

Had my headlight enclosure off to wire up a new front brake master cylinder that I installed on my 79 XS400. Since I put it all back together, I no longer have a working headlight.

Could have been that I shorted something, or just a coincidental headlight death?

I've gone alone with the wiring diagram and everything looks right.

Any leads on how to test this with a voltmeter? If i f'd something up, or the bulb itself is just shot?

thanks.

spectra · Nov 22, 2017

Easiest way pull the plug and see if you have voltage at the plug when the light is on. If not well you have to trace it somewhere. If voltage well light is toast.

spills · Nov 22, 2017

The plug?

My light connects to 3 wires... if i remember correctly: a black that runs to ground, and a yellow pair for high /low beams.

spectra · Nov 22, 2017

spills said:
The plug?

My light connects to 3 wires... if i remember correctly: a black that runs to ground, and a yellow pair for high /low beams.

Yes the 3 wire plug that connects to the headlight. Not sure what is what but one has to be hot..........if it isn't well issues somewhere.

arfstrom · Nov 25, 2017

Stator, to diode, to safety relay, handle bar switch to headlight. Pending which version of bike, that is the path of the So their is a plastic block that might have been put together with a missed connection. Which is in the headlight bucket. (follow the handle bar wire bundle.) Make sure everything is right. Hope this helps, I know this is in the wire diagram section.

xschris · Nov 25, 2017

The 79 is wired different. Check the bulb first by wiring it directly to the battery. If it works check to see if power is going to the headlight relay located by the neck of the bike. The bike needs to run or be kicked over to trigger the relay.

spills · Nov 26, 2017

Okay so the bulb works when I wire it directly to the battery.

Using the 79 manual wiring diagram, I'm a bit confused as to which is the relay as nothing is labeled... seems like it should be the one coming off of the starter switch / fuses, and headed to the light / horn switch after that ?

The relay is the one on the clutch side of the bike, just tucked below the tank?
Can I bench test the relay with just a voltmeter off the bike? or do I need to have it connected to the battery.

Thanks!

BBS360 · Nov 26, 2017

Same side as clutch lever, I believe. My xs360 has a relay in the same place, not shown on wiring diagrams.

I'd check the headlight connector for voltage before going down the rabbit hole. Should be +12V on the green for lowbeam and ditto on the yellow for highbeam.

If not, check out the relay.
That's the only year to wire the headlight relay the way it is. I don't have one but I believe you should get an AC voltage measured across the Yellow and black wires at the relay with the bike running.
I suspect the relay may have an internal diode. Later years have the diode in the wiring harness and it is pretty common for them to blow.
Could be that it's blown inside. A 1 or 2 amp diode from radio shack should do if that's the case.

spills · Jan 5, 2018

BBS360 said:
Same side as clutch lever, I believe. My xs360 has a relay in the same place, not shown on wiring diagrams.

I'd check the headlight connector for voltage before going down the rabbit hole. Should be +12V on the green for lowbeam and ditto on the yellow for highbeam.

If not, check out the relay.
That's the only year to wire the headlight relay the way it is. I don't have one but I believe you should get an AC voltage measured across the Yellow and black wires at the relay with the bike running.
I suspect the relay may have an internal diode. Later years have the diode in the wiring harness and it is pretty common for them to blow.
Could be that it's blown inside. A 1 or 2 amp diode from radio shack should do if that's the case.

Alright, so I have light when I wire the headlight directly to the battery.
Also, If I jump two ports on the relay together, (I wanna say Yellow to Red/Yellow?) I get the headlight to illuminate.

This lead me to believe the relay was shot, replaced it but still no dice.

Any leads here?

NewHavenMike · Jan 6, 2018

I had electrical problems with my bike simply because the fuses and the contacts were dirty, even though they looked OK. I kept the original fuse box with the glass fuses.. I bought new fuses and rubbed the contacts with scotch brite or sandpaper and it everything worked after that.

Another thing to check is the contact points in the handle bar switches, same deal here. The contact point get greasy and corroded and cobwebbed and need to be carefully cleaned and lubricated a tiny bit. I may have used graphite here.

Headlight failure

spills

XS400 Member

spectra

XS400 Junkie

spills

XS400 Member

spectra

XS400 Junkie

arfstrom

XS400 Guru

xschris

XS400 Guru

spills

XS400 Member

Attachments

BBS360

XS400 Guru

spills

XS400 Member

NewHavenMike

1976 XS360C

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