So, the zener diode is the latest in the string of bad parts on my Moby. But there is something that I'm not understanding very well..
When I had the bike running, I noticed that the tail light was on - and quite bright. I tried the brakes, but pulling either brake had no effect on the tail light (at least not that I could tell). From this I assumed that one or both brake light switches were stuck on.
I had to repair the steering on this bike, so I had the zener diode off of it. I was ready to re-install it, and I thought I'd check the zener, just for drill. Guess what? It measures a dead short! This didn't make any sense, so I rigged up a little zener diode tester with a 16VDC wall-wart, and a 200ohm 5W resistor. The tester confirmed a dead short (and yes, I tried it with both polarities). If anyone wants to know, I can tell you how to make & use the tester.
From the wiring diagram, I don't see how this is possibe - to have a tail light lit, with a shorted zener diode in the system. Does anyone know how this could be? And is the motobecane a negative or positive ground system?
If anyone has a spare zener, I could really use it at this point. Any help appreciated on either count.