I'm gonna take a wild guess that the diode is used to shunt inductance from the fan motor (motors are inductive, and can create reverse voltage as the magnetic field collapses).

*IF* that is the case, the cathode goes to positive. Oh, gee, Bill, that helps a lot. Well, the cathode is marked by the band on the diode, the anode is the tail of the arrow in the following symbol:

Ground.....Diode.....+12VDC

(-) -->|-- (+)

If you put the diode in backwards, it will flow BOKU current for a very brief period of time, then it lets out the magic smoke that made it work. If you put it in properly, it will shunt any reverse voltage induction over about .7V.

Caveat emptor on using my advice, which is based on guesses, assumptions, and lately has been evidencing some critical omissions... <img src="/forums/images/graemlins/rolleyes.gif" alt="" /> <img src="/forums/images/graemlins/drunk.gif" alt="" />