Headlight problem (again? still?)

Hello,
I am still running without running lights, as some may remember from my relay thread, but have taken my bike to a local mechanic for help. He is not a BMW mechanic, though he has experience with them and one of his guys is well trained on electrics.

My problem is this:
My headlight and tallight don't turn on when the ignition is fully switched. I have brights and brake lights, but no running lights.

After some evaluation the mechanic told me that everything seems to be in order in terms of wiring, but it is his belief that the dimmer/horn switch on the handlebar is bad. I explained that it merely controlled the brights (to my knowledge as I have no owners manual), but he said all the wiring passed through it and there is some indication things are screwy in the switch. He said they could jiggle the switch and the lows would come on while the horn was sounding, but the light wouldn't stay lit.

Does this sound reasonable? A new switch costs $85-$90 and I obviously don't want to spend the money in vain. Thanks!

you need an owners manual
then you need the big clymers bmw book
if your gonna continue to own a bmw
then you need to learn to work on your own stuff to a point
Im not a armchair quarterback, we dont know what was really tested, what shows good, what has spark when needed, how good the wrench is....
that said
if you trust this wrencher, and he said everything is good to the switch, and after that its funky.....well.....

remember electricity is like water.....it flows
if it gets to point "a", and not past that point, then you got a dam in the way
if all the "juice" is not making it to the tank, then you have a leak someplace, a short, a resistor or a grounding problem

Does this thread give you any additional ideas? Sounds like the problem you're having.

http://forums.bmwmoa.org/showthread.php?t=15905&highlight=headlight

Kurt in S.A.

I appreciate the quick replies. Once again I neglected to state my model, which is a 1974 R90/6, actually manufactured at the end of '73, so I don't have a relay for the headlight.

I appreciate the suggestions. I don't have an owner's manual, as they are hard to come by. I tried to get one from Bob's, but they are sold out. I do own the Clymer manual, but am unskilled and unpracticed at reading wiring diagrams. Hence my questions. I was just double checking that this is a plausible problem/solution before I lay down $85. It seems worth trying.

Thanks!

Alright, I have the same bike and plenty of years of electrical experience so let me see if I can lend you a hand.

Problem: No running light in the tail, no low beams

Consider that these may not be related!

Low beam only:
- Wiggling the switch does not mean it is bad and that is why it caused the high beams to light. You have two wires out of your switch into the headlight bucket onto the board: White (high) and yellow(low). You can check these connections on the circuit board for power. IF you are getting power out to the high beams, then you know that the yellow/white power in wire from the ig switch is good to go.
Where is the likely fault? The yellow wire terminates on the yellow block of the circuit board. A yellow wire from this block then goes to the light. Check to make sure the power is getting to the board and then to the light. IF this is a new onset problem (aka, the wiring did not just re do itself) then your switch is most likely the fault.

No rear running light:
- Your brake light gets 3 wires; Green/black (brake light), Grey/black(running light), Brown (ground).
You are having a fault with your grey/black wire if you are getting no light. If your instruments are lighting up then it is not the circuit board as they use the same output. If you are getting brake lights then it is not the ground wirte as the ground is shared for both running and brake. So, the most likely is that the grey black wire is probably having a poor connection on the circuit board or in the light assembly.

I hope this helps and is pretty straight forward. If you do not have a voltmeter I would recommend getting a cheap one form some where like harbour freight for under $20. It is an invaluable tool.

If it is the switch I have a good used one for that year that I can sell you if you are interested.

Also a continuity tester (with a light) is a great and inexpensive tool. You ground it then go backwards in the circuit to see where you begin to get the 12V for the running light - but you need the wiring diagram as well.

Just my 2 cents

This idea came from this forum...

Have you tried very carefully turning the ignition towards the "off" position while the bike is running? You may reach a spot where the lights come on, and the bike still runs. I had the same issue with my RS, it was intermittent. I needed my ignition switch fixed. And I also needed my handlebar switch replaced as well, but I could actually "run" with the ignition switch slightly "backed off".

Thanks for the other replies, and especially for the offer of the gently used dimmer switch. Unfortunately I already ordered one new before checking back here as I'm feeling somewhat impatient to get the bike up to commuting standards. It is possible the problems are not connected, but the wrencher seems fairly certain this is the culprit. I had considered the ignition switch, but no amount of jiggling will render running lights, and the dimmer switch should be pretty simple even for a novice like me. We'll see in a couple of days when the part arrives and I report back.

Thanks!

DrEvil, I presume, one quick question for you since you have the same bike. I have the new dimmer switch installed, but the only one available is from an earlier year and the wire coloring is different. In place of a red wire there is a green and red wire. When I removed the old unit this wire was plugged into the black and blue section of the contact panel, not the red, which confuses me a little as I thought it was color-coded for a reason. Can you tell me where this wire is supposed to go?

Thanks!

Hey Man,
The red is interchangable with the Green/Red. The only difference in the original wiring for the older switch is that it got its power directly from the ignition switch as there was not a board like in our years. The green/red, or just red should go to the red on the board as this is power in from the ig switch (switched power). I am not sure why someone put the G/R to the Blue/black, that is the power for the RH turn signals. You may wish to check the rest of your wiring.

For your new switch (/5) this is the wiring:
- Yellow --> yellow on headlight
- White --> White on headlight
- Black --> ground for horn
- Other black --> black on board to horn
- Green/red --> Red on board
- Yellow/white --> ignition switch terminal 56

Hope that helps

Yeah, that helps greatly. I'll have to examine all the connections . . . I seem to remember another wire wrapped red but not plugged into a red plug. I appreciate the help.

Forget the owners manual, it's more comic book than maintenance source. Get a Haynes and a Clymers. I had both for my old airheads as one often covered something better than the other did, especially in photos. Wiring is usually straight forwad on the older bikes but they still use smaller guage wires than you might think. Did you by any chance put in a high amp bulb a while back? If so the contact might have melted back into the plastic mount from the heat of high amp draw in the switch assembly on the handlebar. I had that happen on my K bike, the contact flat diappeared into the plastic.

Yeah, I've got the Clymers, and should probably pick up the Haynes. My main problem is that this is my first bike, BMW or otherwise, and these are my first real attempts at complete home maintenence. This is really out of necessity seeing as the closest dealer or authorized repair facility is at least 1.5 hours away. It just seems that these manuals presuppose some familiarity with the bike's systems and don't always explain things sufficiently to a noob like me (for instance in the wiring diagram it labels a wire as "Y/W" coming out of the dimmer switch and "G" going into the ignition switch . . . ?).

Thanks for all the help.

I've found that once in a while a good dose of spray electrical contact cleaner on [in] the offending switch can do the trick. I finally learned through many years of mechanical misadventure to try the easiest things first. Sometimes ya get lucky.rj