1987 K100 RT headlight problems

[mark.roden]

Happy first day of summer all...

Just bought my second bike and second BMW. First was an '86 R80RT. Like my K, so far. 47,000 miles on it. 50 AMP alternator was not charging properly, turned out to be faulty connections. All set with that.

Now, my headlight has been going off. Does come back on. Changed the bulb, same problem. Checked many of the wires and all of the connections to the bulb. Can anyone give me any advice? I read somewhere about LED lights added causing trouble with the relay. This bike has rear brake LED's added and a charge gauge with LED's, my bike mechanic didn't think it was that.

 

[98lee]

Welcome to the forum!

This is going to sound weird. That is a common first symptom of dirty brushes and commutator in the starter. As it gets worse, it will start to affect the starting.

BMW grounds several circuits through the starter including the load shedding relay. When the brushes no longer make good contact with the commutator, all kinds of problems arise.

It's easy to disassemble and clean, just make SURE to mark the housing and end plates so they go back together in the same orientation. It is possible to get the starter to run backwards if one of the parts is rotated during reassembly. Check for adequate remaining brush length. A new set of brushes and holder from BMW is around $30 if needed. Clean commutator with a piece of ScotchBrite.

 

[mark.roden]

Thanks, Lee, much appreciated. This will be my first starter exam rodeo, but me and my well worn clymer manual that came with the bike will get on it.

 

[mark.roden]

Tried starter fix, no results with headlamp. Still out.

Per Lee's advice, I removed the starter, disassembled, cleaned, used scotchbright on the commutator and checked brushes. One brush was worn to the top of the circle, the other brush was worn halfway down into the circle. I understand these are both replaced at once. Put it back together, re-installed and still the same situation with the headlight. Looks like brushes are coming due, but seems like problem with headlamp might be elsewhere? Any other theories on the headlight? Thanks!

 

[98lee]

Sorry that that wasn't it, but you efforts weren't wasted. You should have no starter issues for 10s of thousands of miles now. And it didn't cost anything.

The contacts inside the headlight switch can recede into the plastic housing, especially if a higher wattage headlamp is used. the heat in the contacts melts the plastic a bit. The difference in the height of the contacts can be seen with switch disassembly. Only fix is replacement. Other than bad contacts at connectors, this is the only other thing I can think of. Retrofitting with relays (Eastern Beaver) solves a lot of problems with the headlight circuit including contact recession.

 

[mark.roden]

Eastern Beaver relays already in

Was good to check out the starter. your advice, Lee, seemed very logical. I wish it worked, but, am glad I know how it looks. I researched Eastern Beaver relays and realized my bike already had them installed. I went back and pulled the bulb. I noticed that socket that the bulb goes into in the bulb assembly had overheated at some point. The metal connector that the bulb contacts on the assembly seemed a little burnt too, so I sanded to try and make better contact. Don't think it is the problem(?). I checked the fuse inline from the battery and found one other loose connection in the Eastern Beaver relay connected wires. Still no headlight. Want to take the bike for my first good ride, about 150 miles for a Maine vacation next Friday, so I may be heading to my local mechanic. Before I do that, can I troubleshoot the lines to the bulb with a voltage tester or are there any other things to check? Thanks!

 

[98lee]

Before I do that, can I troubleshoot the lines to the bulb with a voltage tester or are there any other things to check? Thanks!

Sure. Just remember, the headlight (like any other circuit) not only needs 12 volts, it also needs a good ground. A lot of problems on older bikes can be traced to bad ground connections. People will check for voltage, but forget to check grounds.

Try checking with and without a load (the headlight) in the circuit. A bad connection can let voltage through, but not enough current. That will show up as lower voltage when a load is applied.

It's possible that one of the relays may be bad. Do you have high beam?
You can also unplug the Eastern Beaver setup and plug the stock wiring directly to the headlight to see if that works. If so, then the problem lies in the relay system, not the bike.
Check the battery connection for the Eastern Beaver setup.

 

[mark.roden]

Highbeam question...

No high-beams, either. So, maybe not the relays? It appears the way the relays were wired may have nixed the original headlight plug, but I'll look for it again and, if there, will by-pass relays. I am going back in later today to check grounds. I read that the switch for the headlights has all the power coming through it, so I may look that over, too. Thanks, Lee!

 

[98lee]

. I read that the switch for the headlights has all the power coming through it, so I may look that over, too. Thanks, Lee!

Not if you have relays.

Originally from the factory, all the current for the lights goes through the switch.

When the relays are put in, only the low current needed to activate the relay goes through the switch. The high current necessary for powering the lights comes through a separate larger wire straight from the battery, is switched by the relay, and then straight to the lights. Check for this separate aftermarket wire at the battery + terminal.

 

[mark.roden]

Success!

Bad ground to battery, lights are on. Needed to take the negative terminal cleaning one step further. Thanks, Lee. Learned quite a bit for such a simple fix! '87 bike, there's some "stuff" on parts.

 

[98lee]

On new bikes that "stuff" is called crud. On old bikes it's called patina.