87 K75 Electrical Problem

[48882]

I was riding the bike from LA to San Francisco this week. My nephew had replaced the fork seals and I was excited to have the suspension working properly again.

I was stopped at a red light right before turning onto the 405N and I could see my headlight in the reflection of the car in front of me. And then it went out. And then it reappeared! The light turned green and I entered the freeway. When I stopped a couple of hundred miles later, the headlight was out, but the high beam worked. I thought I had just lost the low beam and needed a new bulb.

Toward the end of the ride (I was only going half way on day 1), I noticed that the horn was not working. Additionally, any attempt to use the turn signals (right, left or cancel switch) led to both turn signal flashing once and then going out. Very mysterious! After a night at my buddy's house, I started the bike to finish the trip. To my surprise, the headlight, turn signal and horn all worked properly!

I continued the trip, but before I arrived home, horn, headlight and turn signal stopped working, with the turn signal operating as described above. After the bike sat, they continue not to work.

I think I can rule out anything heat related, and it was suggested that I replaced the fuse, which I did to no effect. Any thoughts on where to start looking for this electrical gremlin?

 

[20774]

Do you have access to a wiring diagram? I'd find each of those components and see what's common between them. Seems to me that it's either a fuse or a ground.

 

[48882]

I did take a peak at the wiring diagram, and I must admit it is too many years since my electrical engineering days in college, I can't really make it out. But by that same logic, the left handlebar switch controls the headlight high beam, turn signal and horn.....

 

[GTRider]

This sounds like a “ground spider” issue, as Kurt mentioned. Current isn’t getting to ground as it should, so it’s backfeeding at the grounding point or simply not flowing. IIRC there is on the early K-bikes a ground connection or cluster underneath the front portion of the fuel tank. That’s the first location I’d check and clean, along with any other ground connections-including making sure that battery to chassis ground is clean and secure.

Best,
DeVern

 

[98lee]

I was riding the bike from LA to San Francisco this week. My nephew had replaced the fork seals and I was excited to have the suspension working properly again.

I was stopped at a red light right before turning onto the 405N and I could see my headlight in the reflection of the car in front of me. And then it went out. And then it reappeared! The light turned green and I entered the freeway. When I stopped a couple of hundred miles later, the headlight was out, but the high beam worked. I thought I had just lost the low beam and needed a new bulb.

Toward the end of the ride (I was only going half way on day 1), I noticed that the horn was not working. Additionally, any attempt to use the turn signals (right, left or cancel switch) led to both turn signal flashing once and then going out. Very mysterious! After a night at my buddy's house, I started the bike to finish the trip. To my surprise, the headlight, turn signal and horn all worked properly!

I continued the trip, but before I arrived home, horn, headlight and turn signal stopped working, with the turn signal operating as described above. After the bike sat, they continue not to work.

I think I can rule out anything heat related, and it was suggested that I replaced the fuse, which I did to no effect. Any thoughts on where to start looking for this electrical gremlin?

Gino (48882),

Your flasher unit that causes your turn signals to flash is powered by fuse #7.

Your horn is powered by fuse #7.

Fuse #7 is powered by the load shed relay.

The load shed relay powers fuse #7 AND the headlight. That is what makes the headlight and turn signals go out while you
are trying to start your bike.

The load shed relay is grounded through the starter brushes.

You have either very dirty starter brushes and commutator OR worn out starter brushes.

Either way, at 120,000 miles, you need to have your starter rebuilt or replaced. I have the parts or good used starters.

Another confirmation of this is your October 14 post.

 

[48882]

I need to take this opportunity to say THANK YOU to @98lee for taking two seemingly disparate problems and finding the true root cause. The commutator was indeed quite dirty. After cleaning and replacing parts with the after market rebuild kit https://www.euromotoelectrics.com/Starter-repair-kit-for-Denso-Starter-BMW-K-p/bmw-strk007tk.htm the bike started right up and the headlamp, turn signals and horn all work. What great detective work!

A slight note on the rebuild kit. While definitely value for the money, we found two problems, small but annoying: 1) the small o ring that insulates the inbound power supply from the starter shell was a little too big. This made it difficult for the o ring to fit in the hole along with the threaded screw 2) the brushes were 50 thousandths too long (relative to the stock part). While this sounds like a trivial amount, it causes the brush to push harder on the commutator and seemed to push the commutator to one side within the plate. After filing the brushes down, assembly was much easier and the started sounded much more like a stock one when power was applied.