Another /6 Electrical Question

[RideSolo]

I do appreciate all the responses to my Fiamm horn and relay question, I didn't mean to raise such a kerfluffle but I think it's been solved satisfactorily. I now have another question:

I'm close to getting my '75 R90/6 on the road, just finishing up some details and odds n ends. The current problem is that I have no head light or tail light. I'll try and lay out the facts as clearly as possible to keep confusion down:

1. New battery (and charged)
2. Turn signals working
3. Instrument lights working as well as the various idiot lights
4. Rear brake light working when you push the rear brake peddle. Front brake lever, no brake light, ordered a new switch, didn't replace it when I did a rebuild of the MC, should have. I anticipate that'll solve that problem.
5. No tail light. Tested the bulb, bulb is good
6. No head light, hi or lo beam. If you push down on the switch for the flash function head light comes on as it should. I also noticed that w/ the switch in the lo or hi positions the blue hi beam indicator light at the bottom of the tach is on, sort of dim. When you move the switch to the flash function the blue hi beam light goes out.
7. The little parking light in the bottom on the headlight isn't working, bulb is good

This morning I ordered the EME wiring diagram that's been recommended, once that's here I can be more comfortable doing more unplugging and plugging in the headlight bucket. AND once it's here to lean on I believe I'll be able to dive in and diagnose with some amount of confidence.

Questions:

Am I missing something stupid like "the engine has to be running for the headlight to work"? (Pretty sure that's not it, but guess it doesn't hurt to ask.)

Is this some kind of known airhead oddity that can be corrected in a couple steps?

[schrader7032]

I'd start with something simple like the parking light. It has two wires to the bulb socket - ground and power. As for power, following the wire back gets me to the fuse in the headlight shell. Fuse good? If so, then do you have power on the one side of the fuse? If not, then you have to find out why. From my Haynes, the power side of the fuse connects to the light relay, the handlebar flight switch (might be UK only), and the ignition switch. If you don't have power to the fuse, then you'll have to work backwards.

[srankin]

On your bike, the taillight and parking light (the little bulb in the headlight) are fused at the bottom fuse. So for the issue with no taillight, start with a fuse check.
That fuse's power comes from the solid gray wires on the other side of the fuse the wires become Gray/black stripe.
So the taillight power wire will be gray/black as will the parking light.
If the fuse is good, then there is a lack of power to the fuse. Use a test probe grounded and look for voltage at the gray wire side of the fuse.

As for the headlight problem, It can be confusing to look at the wiring diagram as the headlight is as I can see not fused at the top fuse but all power shares a common terminal on the circuit board. This is the solid green wire on the left side of the board terminal 15. When the ignition switch is on, power from the red wire flows into the green wires supplying the power for them. Power does NOT go through the fuse for the headlights. On the other side of that fuse is power for the turn signals and brake lights.
Turn signals, and brake lights are fused at the top fuse.

To be honest, headlight relays do go bad and you may just have a bad relay.
I am using the PDF wire diagram supplied in your other post by Wa1nca. St.

R90S+Wiring+Diagram.pdf

(304.82 KiB) Downloaded 41 times

[RideSolo]

Thanx to you both! A few weeks ago I printed out the wiring diagram you posted and I've been wishing I had taken a copy of the file to a print shop to have them print it out in a much larger size. I'm going to wait to get my EME diagram in and go through it. Between now and then I'll investigate based on the comments you both made here and see where that goes. A bit of good news; I have a horn. In an effort not to confuse things I'm going to post a final comment to the horn thread and call it done. As for this issue, in the words of the former Governor of CA: I'll be back

[srankin]

You will be very happy with the EME diagram, they are so far the best to have. St.

[RideSolo]

You are right about the EME diagram. That's a real piece of work and pretty much indispensable. I'm thinking that'll get me moving in the right direction, got it today.

Though I haven't had time to do a deep-dive, I did make sure the fuse is good. Just to be sure, both are now new. I've checked w/ my buddy who's got piles 'o' parts, /6 and otherwise, to see if he's got a headlight relay. He didn't have an extra front brake light switch for the MC but my new one came in the goodie box today.

Also I checked the parking light bulb in the headlight and it was dead. I replaced it w/ a new one but still no park light... HOWEVER, now the park light flashes along w/ the headlight when you use the Flash switch. Small victory.

[srankin]

LOL, if the previous owner was in the headlight shell doing any "repairs" or modifications, it could well look like a bundle of jumping snakes.

Everything is however pretty easy to figure out. BMW color coded everything so as long as your are dealing with factory wiring, everything has its place.

Get a good light, and perhaps needle nose pliers or forceps, a good beer and check to make sure wires are plugged into the proper spots on the board.

You may find the parking light bulb plugged into the wrongs spot.

Good luck, St.

[RideSolo]

As mentioned above I'm welcoming small victories. I replaced the front brake light switch on the master cylinder today and that was successful. Should have replaced it when I did a MC rebuild, oh well, live n learn.

I've got light and needle nose pliers but will pass on the beer, never acquired a taste for the stuff; I always get the impression "that horse has diabetes." Anyway, I do wonder if somebody has replaced the headlight harness at some time. The diagram I got shows the headlight wiring as White, Red, Yellow, & Black/Gray however what's there is Blue, Green, Brown, & Red/Gray. And all four of those connectors are OEM on the headlight end but are crimped on connectors inside the bucket. NOW, it just occurred to me that there's a "Greater Hemispheres made for BMW" fairing, looks similar to a Vetter, that came with it up in the loft of my shop. I'll bet the original was removed to put on that fairing and a different harness, perhaps from a newer model airhead, was put into the bucket when the big fairing was removed. I'll climb up into the loft tomorrow and look to see if the original harness is still living as a part of the big fairing. I don't care as much about the colors as long as what's there plugs into the right places but I'm not happy w/ the crimped connectors. I'm picky about things like that so will probably have to "fix" them even if they are plugged into the right spot. Moving on.

[srankin]

Scotch?

LOL, sometimes the crimped on connectors are the first sign of "previous owner's disease"

The wiring diagram is correct, White, Red, Yellow, black/gray. So the other is wrong, it is from the universal fit fairing.

I will bet if you find the factory harness it might solve some of your problems. FYI, it is possible EME company might have the harness in stock for sale. good hunting St.

[RideSolo]

If/when I drink (not often) it's good bourbon for sure.

All I'm seeing in this case is, almost for sure, the aftermath of the removal of the big ol' fairing. I don't know when that was done, before or after the previous owner. As it sits right now I can live w/ the headlight harness that's there; the colors may be a bit different but I can use the diagram and make sure the right wire is plugged into the right place and be confident w/ it. I've inspected each of the crimped connectors, corrected possible issues, and applied new heat shrink. I am going to keep eyes open for a proper replacement (new, decent used, etc) but it won't keep me from finishing things up for now. Still waiting to hear from my buddy about the headlight relay but he'll get back w/ me when he remembers. For now I'll clean up all the terminals and keep testing. Fingers, eyes, & etc crossed.

And I found a decent picture of the fuse/connector board and printed it out nice n big so I've got an easy view of the individual terminals w/o all the wires in the way. That'll help w/ all my fiddling around.