1975 R75 /6 Grounding Cable
I'm riding along going to the gas station that sells non-ethenonl fuel when my bike dies. I pull off and immediately notice the grounding wire dangling next to the bike. The end had broken that was bolted to the engine case. I pushed the bike to a parking lot and tried to reconnect what was left of the end of the grounding cable. The bike would start and then the generator light would come on and then it would die. I went to an auto parts store and bought a cable that was made for a car so the eyelets in the end of the cable were too big and I'm thought that it should have been grounded well enough, but the same symptoms occurred. I then suffered the humiliation of having it towed home (but my neighbors thought it was a new bike).
Other than getting a proper ground wire and testing the battery (1 yr old), are there any suggestions of what else could be wrong? Could I have damaged the generator somehow?
I did put a battery tender on right when I got home and the light on the battery tender that evening turned green.
Last edited by bscarpenter; 11-06-2012 at 10:25 PM.
I don't think you've damaged your charging system...you can run the bike with a non-charging system (red light on) for as long as the battery holds out. More than like there's something wrong with the connection at the speedo cable boot. That bolt can strip quite easily if over torqued. You can use any other grounding point, say one of the bolts that holds the tranny cover on. You might have trouble fitting the thickness of the cable eyelet onto the stud and still get the nut to engage. But any engine bolt that you can easily find and attach to should be good for temporary...even long term of you do it right.
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'78 R100/7 & '69 R69S & '52 R25/2
mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!
Sounds to me like you need a new cable. I have had great experiences with Euromotoelectrics. Here is a link to the cable for a R75/6:
I would be tempted to do one of the following:
Get a longer ground cable and run it to the lower right transmission mounting bolt or
Ground the strap on a chassis connection, could use one of the subframe bolts.
The stock set up is a poor choice for a ground strap.
Ok, I finally got around to replacing the grounding cable. Had the tank off the bike and started it with no problem. Put the tank back on and no ignition lights. Took the tank back off and started fine. I had the ignition on and jiggled the wire going from the battery to the starter and the ignition lights flashed on and off. I replaced this wire and secured all connections, put the tank back on started the bike and went for a ride.
Right out of the gate, the generator light came on very dimly and the bike lost power for just a second (this happened twice but i figured that I may have run down the battery with all of my testing) after riding for 10 min or so around the neighborhood all seemed normal and I took it out on the road. 15 mi, no problems. on my way back down the last straight away, I poured on the gas to pass a car. The generator light came on and the bike lost power, i let up on the gas and it ran fine. It did this again each time I would pour on the gas, the generator light would come on and I would lose power until i let off the gas.
Any ideas would be greatly appreciated. The battery is less than 1 yr old, but I have not tested it.
IMO, you have entered into the nebulous land of poor electrical contacts. I trust you can figure out how to use a mulitmeter and measure voltages? If not, you will need to learn.
A technique I found especially useful is to look for voltage drops at wiring connections. That is how I found out (with much disappointment) that my ignition switch was faulty. The basic approach is to put one end on ground (engine) and probe with the other, starting at the battery. The battery should, depending upon whether lights are on, give a voltage between 12 and ~12.6V.
That battery voltage is then a reference. The other locations, i.e. starter, coil power, ignition switch, etc. are then measured and the readings compared to the battery voltage. Much over 0.5 V difference indicates a problem.
I did not think this up myself, instead there is a really good electrical system diagnostics book at the Chicago BMW owner club website: http://crbmw.com/rokcart
It is the best 'manual' on electrical system troubleshooting I have found. I have read that Oak wrote or co-wrote most of the manual, which is intended to 'school' you on BMW motorcycle electrics. It has some good information and ideas for basic troubleshooting. Good luck!