Was winterizing both my K75's today ('90 and '91). Adding sea foam and running them to get it through out their fuel systems. Had both bikes running on their center stands. Shut them down. Took Silver out around the block. Came back intending to do the same with Red only Red wouldn't start. Soon as I turned the key on the lights would blink once and then nada. Even the clock went and reset. A guru friend suggested it might be the battery which is fairly old. So I took it out and attached a battery tender. It came right back and went to 14.3 volts. Tried a heater wire across the terminals to stress test it. It got the wire hot but stayed above 12 volts and came right back with the battery tender. Checked resistance from battery lead to ground. Less than 1 ohm. Put a good quality VOM on the battery terminals. Got a reading in the megohms - well there has to be some power bled off to the clock. But when I turned the switch to the 1st position (the parking lights) the resistnace dropped to 1.2 ohms. When I turned the switch all the way to running, the resistnace jumped up to 8.8 ohms. All the fuses appear to be good, i.e. can't see any burned out pieces.

Any thoughts or suggestions as where to start? Only recent work on the bike was to add a "BMW motometer" voltmeter to the system.I will start by removing it from the circuitry. Just a debugging problem. Next would be to look into the dreaded starter motor short circuit. Though the fact that the voltage drop starts when the parking lights are turned on would argue for other issues.
Thanks for any thoughtful suggestions.
J.

Your clue is in the clock resetting. 

Something interrupted the supply to the clock.

But its permanently live so check the battery connections and earth. The fact that it came back at full volts also suggests this, as in the earth got interrupted for some reason. If not that then possibly the battery is heading out the gap but more likely a connection issue.

Another possibility is the big plug at the back of the clocks is loose and interrupted the power and signals into the cluster.


Edit: I just re read the original post and even that says the battery is old.......bought one recently for my RT about €45........but to be honest park it up and just get a replacement in the spring.

Clock resetting is a clue.  As Olaf pointed out, something interrupted the circuit.  Weird electrical problems are generally due to grounding issues.  I'l guess that this issue you're seeing is due to a bad starter, probably brushes.  Try back spinning the rear wheel and try again.  If the bike suddenly starts working again, then remove and refurbish the starter motor including replacing brushes.

92KK 84WW Olaf wrote:.......but to be honest park it up and just get a replacement in the spring.

I ride year round. Though in truth winter ain't as much fun.

"I ride year round. Though in truth winter ain't as much fun"

Makes you a much better rider come the summer though 

Why not swap the battery from the other bike and see what happens - could be an easy way to start testing before diving into other issues.

Good luck.

Gaz wrote:Why not swap the battery from the other bike and see what happens - could be an easy way to start testing before diving into other issues.

Good luck.

That's waaaay too smart for me.   Actually I cleaned the starter carbon out and switched batteries. Started right up. So now I get to go outside and restore all the things I disconnected in my search for the gremlin. Which brings me to the next issue, BATTERY. What and where to get it. My bud says he's getting in some Odyssey PC680's this week. If I want to pony up USD $140. But at the moment I'm doing an internet search thinking maybe get one off EBAY so I can use points from my credit card to pay for it. I kinda regard that as being free or almost. In this pandemic thingie (fingers making the hex sign) I'm being forced to use credit cards instead of cash so I've been gaining points which I don't use in normal life. Pandemic besides being a major pain where I sit is forcing me to make changes in life long habits, like paying cash.

Hey thanks for the input. And let me know if you know of a decent K75 battery on the internet.

Motobatt - made in Jacksonville FL, as it happens. Not sure if the K75 takes the same battery as the K100, but I've had one in Low Flying Brick for ten years+ by now. Like you, I am (was!) a year-round rider so it's been getting some abuse. I like them enough to have dropped one in Kostenlot (K100RT) and Mfanwy III (850-T3 California) as well.

jjefferies wrote:

92KK 84WW Olaf wrote:.......but to be honest park it up and just get a replacement in the spring.

I ride year round. Though in truth winter ain't as much fun.

Just to clarify.....I meant get a replacement battery in the spring.

Sometimes I get forgetful and get another K in the spring.....