Headlight On All The Time 1981 XS650SH

[ssjody]

I have read several times that on an 81 XS650H that the headlight doesn't come on till the engine starts. Mine comes on as soon as I turn the key on and I'd like to get to the bottom of why mine doesn't work as originally intended. I've been through the electrical system pretty thorough. I put a new original style harness on it when I 1st bought it that I got from MikesXS. The headlight was behaving the same way before I changed the harness, where it would come on as soon as the key was turned on. I have all the original pieces like the lighting reserve lighting unit, headlight relay, original switches etc. completely stock. I've been studying the wiring diagram but I'm having much luck figuring out what the problem is. Anyone got any ideas on what might be the issue?

 

[Jim]

Look at the safety/lighting relay. you can jump around the "lights on" function of the relay to bypass it and lights will be always on.

 

[Jim]

Here's the lighting relay. If someone's jumpered like shown, the lights will come on with the key.... as you describe.

 

[ssjody]

If someone's jumpered like shown, the lights will come on with the key.... as you describe.

It doesn't have a jumper

 

[Jim]

Unlikely, but it's possible the relay is stuck closed. You can disconnect it and ohm across the blue/black and red/yellow pins. It should be open. If you get continuity, the relay's bad.
If that's not it, it's prolly up in the reserve lighting unit somewheres....

 

[Jim]

Btw... if there is a jumper, it's most likely on the (harness side) connector and not at the back of the relay.

 

[ssjody]

ohm across the blue/black and red/yellow pins. It should be open

It is open at the relay between blue/black and red/yellow. Is there a test for the Reserve Light Unit?

 

[ssjody]

if there is a jumper, it's most likely on the (harness side) connector

It's not jumped at the harness either.

 

[Jim]

Headlight power goes from the fuse (R/Y) to the headlight relay. From there, B/Bl to the reserve unit. From there, out to the h/light switch and on to the headlight.
In other words, power has to pass through that relay. With the relay disconnected, turn the key on. Headlight come on?

 

[ssjody]

With the relay disconnected, turn the key on. Headlight come on?

Interesting. Yes, with the relay disconnected it does come on

 

[Jim]

OK, so somewhere in that harness, that H/light relay has been bypassed. Now it's just a matter of using you volt/ohm meter to find out where.

 

[Jim]

If/when you find where the power's been bypassed.... it might be because the H/light relay isn't closing and they just jumped around it instead of replacing it.

 

[ssjody]

they just jumped around it instead of replacing it

It's a new harness from Mikes and I haven't added any jumpers. There's no jumpers in the headlight bucket or in any of the relays or the RLU.

If I'm reading the wiring diagram correctly the Blue/Black wire is powered by the Red/Yellow as you mentioned. The Blue/Black then runs to the RLU. The Blue/Black also powers the Tach and Speedo backlights. When I power on the key with the relay disconnected I'm getting power in the harness at both the HL Relay Blue/Black and at the RLU Blue/Black. I'm not however getting power to the backlight Blue wires up in the Headlight bucket which seems to point to an incorrectly wired harness. The backlight not working for the Tach and Speedo was the real reason why I dove in to begin with. This isn't surprising. When I originally put this harness on I found another wire that was pinned wrong.

This is how my original harness was wired whichI believe this is how they were supposed to be wired from factory because it matches the diagram.

 

[ssjody]

I should clarify that I realize that I should NOT have voltage at the Blue/Black wire at the relay when the relay is disconnected but I do. My reasoning about not having voltage at the Tack & Speedo backlights was purely pointing out that I don't have continuity to the tack and speed where I should.

 

[5twins]

My buddy had a similar issue with the MikesXS replacement harness for his '80 SPII (headlight came on with the key). He tracked it down to a switched power wire in the harness being connected to the Blue/Yellow that runs from the RLU to the hi/lo switch. Normally, this wire is fed power from the Blue/Black in the RLU, and only getting that power when the safety relay is triggered. The power you're seeing all the time on your Blue/Black wire is probably backfeeding from the Blue/Yellow inside the RLU.

I'm not sure why your instrument lights aren't working. Normally, power for them branches off the Blue/Black wire BEFORE it gets to the RLU. I think that pic you posted of your original wiring shows that.

The RLU feeds power to the hi/lo switch on one of two wires. If the headlight is good, it feeds the power on the Blue/Yellow wire. If the low beam burns out, the RLU "does it's thing" and switches the feed to the hi/lo switch to the Blue/Green wire.

 

[ssjody]

My buddy had a similar issue with the MikesXS replacement harness for his '80 SPII (headlight came on with the key). He tracked it down to a switched power wire in the harness being connected to the Blue/Yellow that runs from the RLU to the hi/lo switch. Normally, this wire is fed power from the Blue/Black in the RLU, and only getting that power when the safety relay is triggered. The power you're seeing all the time on your Blue/Black wire is probably backfeeding from the Blue/Yellow inside the RLU.

I'm not sure why your instrument lights aren't working. Normally, power for them branches off the Blue/Black wire BEFORE it gets to the RLU. I think that pic you posted of your original wiring shows that.

The RLU feeds power to the hi/lo switch on one of two wires. If the headlight is good, it feeds the power on the Blue/Yellow wire. If the low beam burns out, the RLU "does it's thing" and switches the feed to the hi/lo switch to the Blue/Green wire.

That's good info and I'll explore that. Might be a common problem on these harnesses.

 

[ssjody]

I performed an autopsy on the MikesXS wiring harness today. Figured out why my instrument lights wouldn't work and why my headlight come on as soon as I turned on the key. The two blue instrument wires was just one wire looped from one instrument lamp to the other in the harness (see image). I also found exactly what 5twins buddy had found that the blue/yellow wire was wired to a switched power. That's a total of four problems in all that I found with the MikesXS wiring harness. I sourced a good used wiring harness and all my wiring problems went away. Everything works as it should now.