Hey everyone!
   I (think I) fixed my problem!
   The entire time I've had my 1985 K100rs, my bulb warning light has been coming on intermittently. I'd occasionally go 300 miles without seeing it. More commonly, it was every 5 miles. A tap of the brake lever would always turn the light off, but it always came back.
   I tried all the usual things; I replaced all light bulbs, cleaned and deoxited all connections. Nothing worked. Yesterday, I finally pulled the Bulb Monitoring Unit out and opened it up. At three of the joints between the connector blades and the circuit board, the solder had cracked. The blades were wiggling freely. Seeing that made me surprised the BMU was working at all.
   After re-soldering all the joints (including the ones that still seemed good), I took the bike out for a quick 50 miles. No warning light  
   Of course, the problem might not actually be fixed. The warning light could still come back at any time. But I really think I got it this time.
   I figured I'd post this message since I can't imagine I'm the only one with this issue. Hopefully, someone else can benefit from my trial and error.
   -Jon

good solve john

we have seen this happen before ..but seems rare

Great catch, thanks for sharing.

Heavy or large components (transistors, relays, capacitors, etc) soldered to a circuit board + vibration + time = cracked solder joints

Good work.

A quick and cheap fix!

I removed my BMU and fitted LEDs to the rear, they never seem to blow. No problems with any lights on the dash now.