Electrical Gremlins!

This is an intermittent problem the bike (an 87 K75s 46k) has been having for the past two months. Occasionally the lights will go out; that is, headlight, rear running light, instrument lights. The high beam flasher still works, as do brake lights, turn signal and horn. And they stay out. This is not a flickering or a dimming; I've ridden 60 minutes without lights (no fun) and then poof, everything comes back on 50 feet from my driveway. And this happens completely out of the blue; it can go weeks without showing up.

Initially, I was told this was a dirty starter problem. I cleaned it and it was just barley dirty. I suspected the load shed relay because it seemed to be the only component that controlled all of these lights, but tests seem to indicate that's not the problem. There is power coming from all the right ports under the load shed relay (I forget the numbers). And the relay clicks when powered. Furthermore, the relay cuts the high beam flash out as well, with the starter button engaged.

I bought a colored wiring diagram, but there are so many interconnected components, I'm not sure where to look next. So before delving deeper into the arcane electronics I offer this food for thought. Any ideas/similar past experiences?

Thank you in advance,
Mike

Have you checked the output from the load-shed relay when the bike is in the failed condition? If not - you may be chasing an intermittent.. first step is finding where the power stops, then figuring out why.

I found several shorts in my system. Take the tank off and look in the fuse box where all the relays are. Check closely for any PO splicing or funny wiring. It drove me crazy for a while until I found bad wires.

Smacks self in head with test light

Thanks, Don. You're absolutely right; I DID test it while it was working and it most definitely is an intermittent. Funny how all your (my) sense gets washed away by spring time and desperately wanting to ride in the nice weather...

So now it's just a matter of waiting for it to fail again. I've been checking several times a day, though not riding due to the snow/ice around here. Of course it can't fail when it's convenient.

Carquz: I've been through the bike several times and no PO splicing, that I can tell, except for the rear right turn signal. It's pretty clear the bike was ridden as a sled on the right side. The cover up job wasn't too bad, though.

Update

The other night the lights went into fail mode again, but came back on before I could get anything done! After getting the bike back together, another issued cropped up: the fuel pump isn't getting power. Actually, none of the wires in the connecter to the fuel tank are hot.

I believe the ICU is kaputt. The ICU gets power, but it doesn't send it out to the control side on the FI relay (yellow/brown wire). The relay does not click while plugged in (removed the cover and watched it). However, after removing it from the bike and applying test voltage and ground to the control side, it did work. And when the yellow/brown wire is grounded with a test light, the relay does work.

So, is it time to shell out 250 for a used ICU (non returnable, of course) for a bike that seems to have been struck down by the electrical gods? Or, am I missing something here?

I would be very reluctant to shell out the money, since in the many years I've been around 2-valve K bikes, I can count the number of failed ICU's I've heard of with the fingers on my head - ie - none. To confirm it is the ICU, I'd suggest borrowing one from a friend. If you can't find one to borrow - give me a PM and I'll ask a friend who may have one or two laying around gathering dust.

I'd still be somewhat suspicious of the starter given the symptoms. Sounds like the load-shed relay is load-shedding when it shouldn't be. That is usually caused by a leakage path through the starter.

Hi, Mgalie,
Listen to Don! I had the same problem you describe - lights flickering and questionable fuel pump. In my case, it was my own stupidity. When I had done the clutch spline lube a couple of months ago, I had tightened the starter lug hand tight, and then forgotten to righten it with a wrench! When I went to remove the starter to clean it, the wire moved as soon as I touched it. I tightened it with my 10mm wrench and have had no further problem. My load shed relay was shedding when it wasn't supposed to. Tightening the connection stopped it. I would bet that, in your case, it is a starter issue, either dirty or needing brushes replaced. Good Luck!

PHMarvin said:

Hi, Mgalie,
Listen to Don! I had the same problem you describe - lights flickering and questionable fuel pump. In my case, it was my own stupidity. When I had done the clutch spline lube a couple of months ago, I had tightened the starter lug hand tight, and then forgotten to righten it with a wrench! When I went to remove the starter to clean it, the wire moved as soon as I touched it. I tightened it with my 10mm wrench and have had no further problem. My load shed relay was shedding when it wasn't supposed to. Tightening the connection stopped it. I would bet that, in your case, it is a starter issue, either dirty or needing brushes replaced. Good Luck!

Click to expand...

Yes do listen, there is a reason he is known as THE Don..........

Bobmws said:

Yes do listen, there is a reason he is known as THE Don..........

Click to expand...

Yes, thanks for the advice: I've been haunting this list long enough to know that Don's hunches are pretty reliable. I only had enough time today to tug on the starter connection: it was tight. Tomorrow, hopefully, I'll slip it out and look at the brushes again. And if all looks well there, I guess just wait for the lights to fail.

Take this with a grain of salt, since I'm not the brightest guy around, but I once had a main fuse crack (not blow, but the metal just cracked) and the resulting sometimes on, sometimes not was really hard to track down. Also I had a battery cable corrode once to the point where the alternator was running with effectively no load, which caused some really weird problems... neither was on a BMW though.

I'll keep my fingers crossed for you, electrical gremlins are some tough critters.

Andrew
'95 K75

Look for an open not a short!!

What you have is an intermttent open circuit. Not a short circuit. A short circuit would blow a fuse and the lights would not come back on ever. Since they come back on whenever, Something is removing power, then re-applying without shorting to ground. Maybey the fuse is making and breaking from vibration, or bumps. Check all plug connections as well. Hope this helps!