Saturday, October 11, 2014

Headlight Weirdness by Brigitta, Resolved.

Back when I replaced the speedo/odometer on Brigitta, my '87 R80, I happened to notice that sometimes my headlight remained on even when the key was off!  Weird.  At the time, I attributed the headlight behavior to me messing about the wiring involved around the headlight area.

It sort of remained in the back of my mind however, and this morning I took a closer look at things.

One obvious thing as I moved her front wheel back and forth, the headlight would come on when the wheel was turned all the way to the right!  Yep, with the ignition off.  Heck, with the key out!  Obviously, a circuit was being completed somewhere, independent of the ignition switch.

Off came the headlight so I could get at the ignition wiring.

Ignition switch wires

Saw some bare spots on the wires, thought it'd be an easy fix.  Trouble was though, as I checked things by wiggling on the connectors, the headlight didn't come on.  Hmmmmm.

I followed the wires into the plastic tube which housed all four wires, wiggled that and the headlight would come on when I moved it in different directions!  Aha!  

So I removed the battery's negative cable from it's grounding point on the engine case so I could work on things without making sparks fly.

Started off peeling the plastic tubing away, and exposed burned/melted red and green wires.  Red of course is hot or power, green is usually ground.  The insulation had burned/melted off both wires in multiples spots, allowing the wire underneath to touch and complete a circuit when bent a certain way.

I kept peeling away the outer plastic further and further along, more burned and melted plastic insulation on the red and green wires!  Two attempts at just patching what I had exposed just resulted in the headlight being on all the time when I would reconnect the negative cable on the battery.  Not good.

Off came the negative wire again and off came the gas tank, I pulled the connectors off and pulled the wires out of the headlight bucket, continuing to free it from cable ties until I reached a four connector plug into the main wiring harness.  

Once the cable was free, I removed the entire outer tube.  I ended up removing all the melted red and green plastic, leaving both the hot and ground wires complete bare.  Once I had all four wires separated and cleaned off, I used electrical tape to re-insulate the now bare hot and ground wires, ensuring there was no contact between them anymore.  Each wire I re-insulated, I tested by touching the grounding strap on the battery to ground, no spark meant no contact!

Tidied things up with more electrical tape, re-forming it into a single wire bungle which I threaded back along the cable path and into the headlight bucket.  Got everything connected back up, negative cable in place, no headlight coming on when swinging the front wheel all the way left and right!

Tested the ignition switch, lights came on when I turned the key as expected and she fired up when I pushed the starter button so the connectors were correct on the ignition switch.

No more mystery headlight turning itself on for no reason!  I did take more pictures, but bare wires are just that, bare wires!  I lucked out, the melted wires had connectors on both ends which were in good shape, and it was a relatively short run of wires, perhaps 18 inches; so not a lot of ruined insulation to remove, not a lot of new electrical tape used to form new insulation.

9 comments:

David Masse said...

Nice work. I wonder why the insulation melted to begin with. The wire gauge could be inadequate for the amperage the headlight is drawing, no? My knowledge of electricity is really rudimentary, but there could be something wrong with the circuit design.

Richard M said...

On the airheads, ground is brown and green is switched power. With a red and a green bare wires touching, it may have been more than your headlight switching "on" when the bars were turned. I usually had broken wires probably due to age but the wires inside the headlight bucket were probably getting hot from the headlight. Better that than a short to ground. That may have caused a fire!

Charlie6 said...

David Masse, I tend to be leery of electrical gremlins but this one proved pretty straightforward. As to cause of melting, I have no idea.

RichardM, I stand corrected re the wire color codes. All I knew was each time the green and red wires touched, the headlight came on. Dont know if heat from headlight was the cause though, the melting extended all the way back to the connector on the wiring harness....not a fuse in the circuit either....

Charlie6 said...

David Masse, the wires powering the headlight were a different set of wires, I think the wires that melted were what powered the relay that allows power into the headlight circuit.

Canajun said...

You're lucky it was a pretty straightforward problem and fix. I'll tackle anything on a bike without a second thought, but I hate dealing with wiring issues. At any rate I'd still be concerned about why the insulation melted. If the problem was too much draw there could still be cause for concern from overheating. Might be worth a little more investigation. Or perhaps I'm just paranoid.

Trobairitz said...

Good thing you are patient. Glad you got it sorted.

Charlie6 said...

Canajun, I too wonder what caused such a huge current draw on that wire bundle to cause the melting....we shall see.

Trobairitz....me? patient? patient would have been taking the ruined cable bundle out, ordering a new one from BMW, and waiting for it to arrive....thanks though.

VStar Lady said...

Wiring issues are such a mystery .. good for you for solving it. Truly impressive.

Charlie6 said...

V Star Lady, not that impressive, it was a discrete wire bundle...and I got the color codes wrong! ;)