The bike in question is a '96 R1100RS, that I helped a friend with this past weekend. It had been sitting for about a year, and we cleaned up wiring. It had several electrical accessories installed - a Kisan Signalminder, LED taillight and brake light, extra LEDs on the luggage rack, and a Centech fuse panel with power switched thru a relay, triggered off the taillight wire. Here's the weird part......
The LED taillight did not work. When we pulled the wire off the taillight, we could measure +12V on the wire. But plug it back in, and the voltage went to 0V. The Centech relay would work fine with the LED disconnected, but would not energize if the LED was plugged in. I plugged in the standard incandescent taillight from my '94, and it worked fine. Seems like just a bad LED, probably shorted out, right? But then we tried this sequence:
1. Plug in LED - no light, no power at the connector, Centech relay does not energize.
2. Power off, plug in incandescent light, power on - no light, no power, no relay.
3. Power off, nothing on the end of the taillight wire, power on - got +12V, relay energizes OK.
4. Power off, plug in incandescent light, power on - light on, go +12V, relay energizes OK.
We repeated the sequence several times. Trouble always started with plugging in the LED. If we went straight from LED to incandescent, it didn't work. If we powered up with nothing on the wire in between, it worked fine. It acted like the LED triggered some sort of circuit breaker, that would reset if we powered up with no light at the end of the wire. I don't see anything in the wiring diagram that would cause this behavior. Any ideas?