I’m looking for some guidance with an intermittent electrical issue on my 1974 BMW R90S. The engine cut out, and all the lights and instrument indicators went completely dark. Moving the handlebars restored power, and the bike restarted immediately.
While investigating with the ignition on, the instrument cluster lit up normally. Turning the handlebars to the left caused the oil light to go out. Returning the bars to straight usually brought it back on. With the bars fully left and the oil light out, manipulating the wiring bundle entering the back of the instrument housing brought the light back on. That led me to focus on that wiring and connector area, although I haven’t established whether the oil light issue and the complete electrical shutdown share the same cause.
I have since removed the speedometer and tachometer housing and disconnected the electrical plug by removing its center retaining screw. The screw was secure, and I found no obvious bent pins, heavy corrosion, burning, or visible wire damage. Although the plug felt firmly attached, I’m wondering whether there could be a poor terminal connection or a damaged wire inside the bundle.
During removal, I loosened two of the three mounting bolts and completely removed the third. That bolt now goes into its hole without catching any threads, so I suspect its threaded attachment may have moved or come loose inside. There are also cracks around several rear-cover screws. I’m planning to carefully remove the cover to investigate the mounting issue and inspect the internal connections. So far, I haven’t confirmed the electrical fault or replaced any parts.
I would appreciate any guidance on where to look next, how best to test the connector and wiring, and what to watch for when opening the housing. I’m trying to work through this carefully and recognize that I have plenty to learn. I can provide pictures if they would help. Thank you for sharing your experience.
> The number one recurring issue I find is corroded connector terminals. Owners who have lived with a favorite Airhead for a LONG time simply lose sight of the fact that their favorite ride is being attacked by time itself. In your specific case, this bike is 52 years old ! That's over a half century !! Or another way to get this to "sink in" is to remember how many cars from 1974 you saw on the road last week ? The fact is, you were lucky if you even saw one car from 2004... a full 3 decades younger !!
The Germans do build a very nice electrical system, with materials and coating much more advanced than the English or Japanese. But you must remember that when these bikes were "king of the road" back in their day, they were ridden cross country multiple times in all sorts of weather. And then endured countless weekend bike washes.
I say this to highlight that water (from both rain and wash) is what causes connector corrosion. It happens at the microscopic level and advances VERY slowly. So slowly that you don't notice. And it does not look like the "bloom" common to battery terminals.
The cure is simple and cheap, but somewhat time consuming. Start today by applying a thin coating of a anti-oxidation compound for electrical connectors to EVERY electrical connector you can reach. The compound I recommend and use is called No-Ox-Id by Sancem, and can be usually purchased in Amazon. This compound 1) fights corrosion common to brass connectors AND 2) excludes water that makes the situation worse. You'll wipe a small volume onto each male connector terminal approximately the volume of an airgun BB, and then re-plug the connector. The volume is so small that the smallest 10cc tube you can buy is enough for 3-5 whole motorcycles.
Remove (unplug), coat lightly, and re-install all the following...
- All plug connectors
- All ring terminal connectors
- Both ends of those pointy German fuses
- All the terminals of the ignition switch
- All terminals of EVERY relay
- Horn terminals
- Even the bulb bases in the turn signal pods and tail lamp (not the HL bulb)
- BOTH ends of BOTH battery terminals
In short... EVERY electrical connection on the bike
You don't need to do all this in one sitting. Start in and around the headlamp where you suspect the issue is. Then do under the tank next time you have the take removed. Then do the blinkers and tail lamp when you install a LED brake lamp bulbs. This must become a habit so that when the front cover is off for the next tune-up, all the connectors for the alternator and points get treated. You get the idea.
> If this is not your problem, while doing such detailed examination you may stumble across a frayed wire or other such issue.
Hope this helps.
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
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