In a previous post concerning electronic ignitions, I wrote that I used a digital Boyer ignition on my 1979 R100. The only issue with this device is if it looses power, even for an instant, the ignition shuts down while the digital part reboots. And that's what's happening. Once on every ride I'll be sailing along and then with no warning the bike simply quits. This has left me searching high and low for a broken connector or frayed wire; something that might make the power go out momentarily.
On the last ride the ignition went out twice in 200 miles, so the issue is getting worse. Add to that the starter was not responding with each button push. That gave me the idea to research the starter relay, located under the fuel tank on the left side (opposite the regulator).
When the relay was removed I found the cause of the poor starting and the intermittent power issue. The relay was full of crud from years of road duty, causing the poor starter button response. The intermittent part was caused by how the relay was connected to the harness.
At least on the 1979, BMW brought positive power (Red) to the relay on one terminal. Then on a second terminal (Red), power is brought out and taken up to other places on the bike. The effect is that 1) the starter relay MUST be installed or power never gets to the remainder of the bike. And, 2) any corrosion or other current limiting issues on either one of these terminals limits the power available for all other lights and accessories.
Photo: The 2 copper terminals join the battery to the ignition switch
The troubling part is this is not "standard" relay wiring. If one had a loss of electrical power, one would not normally look at the starter relay and its socket for resolution. And being under the fuel tank it's out of sight and not something that would come to mind on the side of the road. So next time the tank is off, you might unplug your starter relay and check it out.
🙂
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
Similar story with me. I climbed aboard my '77 R100/CS one day after work recently, and the electrical system was dead. Even the clock. After hauling my sorry self and bike home I pulled off the tank, pulled off the starter relay for inspection and found the leads and some wires coming in were totally green with corrosion. Cleaned it all up, fixed one particularly dodgy wire (cut off damaged part, stripped to expose clean wire, reattached to connector). And everything lit right back up and started up fine.
One other kind of weird thing though, was that I had to charge up the battery as it had been drained down to below 8 volts. So something must have been drawing the battery down like mad while I was at work that day. That's still a puzzle to me. All seems fine in the few weeks since, and the battery is charging normally.
One other kind of weird thing though, was that I had to charge up the battery as it had been drained down to below 8 volts. So something must have been drawing the battery down like mad while I was at work that day. That's still a puzzle to me. All seems fine in the few weeks since, and the battery is charging normally.
I suggest opening up the starter relay can and having a look. Since the starter relay is situated in the electrical path between the battery, and ignition switch, when something goes wrong inside the relay, the ignition switch does not have to be in the ON position to draw power. And problems in this area will not blow a fuse.
On my bike, the original relay had a metal cover, which was growing all sorts of corrosion between the cover and other metal parts inside the can. A short circuit through corrosion could easily present itself as a high resistance load, similar to leaving your tail lamp ON all day. This is part of the attraction of fitting a new relay with a plastic cover.
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
Added 2 photos to first post.
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
After reading Mike Hammer's 1995 article on the starter relay on IBMWR it all became clear to me how the corrosion started, and why this issue may be common to all /6 and /7 bikes with disc brakes. This relay sits directly below the brake master cylinder. Any brake fluid that manages to leak out attacks all the electrical connections around and under the master cylinder. We then rebuild our leaking master cylinder without ever thinking to check the damage to electrical parts that sit around them.
Mike ended up replacing his starter relay with one from an automobile, solely based on the (then) $60 replacement price from BMW. However, 1995 was pre-internet search and shopping. These days you can let Amazon do your heavy lifting for you and find a relay for about $7 that is completely plug compatible with the existing electrical system.
On my bike the issue of the corrosive brake fluid showed up on the starter relay. Luckily a "Dual 87 mini-cube relay" was easy to source, but there was also damage to several other connections as well. On other bikes this could just as easily show up as a charging system error if brake fluid got onto the voltage regulator terminals.
Link to Mike Hammer's 1995 article.
Hope this helps. 😉
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
I've done mike's AR-152 swap.
I wrote up for my shop books additional notes and drawings, correlated the stock bmw relay with the AR one, then labeled my relay & re-designed the bracket to the bike and carry 'THAT' relay as a spare. it's now a plug'n'play if needed 'on the road'
One other kind of weird thing though, was that I had to charge up the battery as it had been drained down to below 8 volts. So something must have been drawing the battery down like mad while I was at work that day. That's still a puzzle to me. All seems fine in the few weeks since, and the battery is charging normally.
i saw your air email request and that issue should be investigated until you have it solved. start by isolating the things that do not effect the running AFTER the relay. what happens downstream from a circuit can draw the system down. not that you'll be able to find it now that it's working. when it fails is when you search again.
This relay sits directly below the brake master cylinder. Any brake fluid that manages to leak out attacks all the electrical connections around and under the master cylinder. We then rebuild our leaking master cylinder without ever thinking to check the damage to electrical parts that sit around them.
ALL the more reason if you still have an under tank M/Cyl. that you check it 3-4x's a yr for leaks. they can be rebuilt fairly easily, re-sleeved if/ when necessary
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