85 K100 RT Electrical Issue

My 85 K100 RT has developed an electrical issue that I will be investigating in the days to come.

Last weekend I noticed that when engaging the turn signals, the signal indicator would flash rapidly. Both sides behaved the same. Upon arriving home, I found that the headlight and signal lamps were non-functional. However, the brake light did continue to work.

Turning the bike off and back on, resolved the issue as the headlamp and turn signals returned to normal operation.

I reseated the connector for the computer as oxidation there causes weird issues from time to time.

Today (Sat), I headed out for a ride, double checking the lights before departure - all seemed good. Went less than a mile to the nearest gas station and the bike would not start after fueling. Headlights and signals were dead. Pressing the starter button would engage the fuel pump (as expected), but would not engage the starter. Toggled the key on/off a few times and the started engaged and started the engine. Lights were non-functional, but I was able to return home.

Further investigation in the garage, the first position of the ignition will light the parking lamp and the tail light - headlight is off. Start/Run position turn all lights off - pressing the starter engages the fuel pump but not the starter. Resting battery voltage is 12.58V.

I'll be looking through the Clymer's manual this evening and investigation the trouble as time permits.

Any thoughts/experience that would expedite the process would be greatly appreciated.

Thanks,
Monte
85 K 100 RT

Most likely, the problem is dirty ignition switch contacts, dirty kill switch contacts, or dirty starter brushes/ commutator.

See details in Kbike Tech Library at the top of the Flying Brick section.

To test for dirty ignition switch, turn ignition and kill switch to on, take volt reading from top right hole in the back of #1 fuse. Compare it to voltage across battery (key and kill on) If difference more than .3V odds are ignition contacts dirty.

My guess, based on your symptoms is the starter, but could be any of them.

Easiest to clean is the kill switch, starter takes the longest. I would do all three just to be sure all is well.

Thanks Lee.

I suspected the switches and possibly something in the starter circuit since it turns off the lights.

The rapid flash of the turn signal had me confused.

It has been a while since I cleaned the ignition and kill switch.

The starter has been on my todo list for a while, but has not made it to the bench for attention.

Now's as good a time as any to tackle all of those.

We'll see how far I get on things tomorrow.

Thanks,
Monte

Rapid turn indicator indicates burnt out turn signal bulb or bad/corroded socket, just like on cars prior to leds.

The headlight is powered through a "load shed relay" which turns lights off when the starter is energized. That relay coil is grounded through the starter so that when the starter is energized the relay turns "off" to extinguish the headlight while the starter is cranking. A dirty starter can cause a bad ground for the load-shed relay coil and make the headlight wonky.

The ignition, kill switch and starter have all been cleaned and the voltage drop from through the switches has been reduced from ~0.45V before cleaning to ~0.34V after cleaning.

Currently no problems with the lights or starting for the dozen or so times since putting it all back together.

The kill switch was certainly the easiest and was indeed on the dirty side.

The ignition took the most work as it required removing the bodywork and tank to disconnect the ignition assembly. I took the opportunity to work the other connectors and clean up the common frame ground while the tank was removed.

The starter was by far in need of the most attention, but is now as shiny as new. It also looks like I'll be in the market for brushes sooner than later, as the one connected to the positive lead is around 7mm (not far from the service limit of 6mm).


As for the symptoms, I thought that I remembered about the headlight being disconnected via the load-shed relay through the starter. I didn't think that the dirty switches/starter would cause the signal to flash rapidly or the headlight to be turned off while the engine was running otherwise. More info to add to the knowledge base for next time.

Thanks again for the insight.

Monte
85K100RT

The headlight going out while riding is a symptom of a dirty starter. I have never heard of the rapid flashing of the turn indicators being attributed to dirty ignition or kill switch or dirty starter, just bad bulb or corroded socket.

Good info to know.

It's interesting that both the headlight and signal issue have seemed to come and go together. Hopefully they're both fixed as well.

Otherwise, I'll be back for another round of ask the experts.

montec said:

Otherwise, I'll be back for another round of ask the experts.

Click to expand...

Let us know what they say. In the mean time you could always ask us.

Let us know if the turn signal was also corrected.

I think I can see how an intermitant ground could possibly cause all the symptoms as well. I'll try to check the schematic tomorrow. The '85 is abit different than other early Ks.

Sorry for the delay in posting an update . . . Was looking for an old post and found that I never completed this thread.

Cleaning the starter solved the issue with the lights.

Monte
85 K100RT

Monte,

Thanks for the follow up. Now we can all add the turn signal problem to the list of possible symptoms of a dirty starter.