Thanks everyone for all the help/suggestions. Here's the follow up:
Finally decided I was spending way too much time thinking about this and called Atwood/Fantastic (used the 800 number on the Fantastic web site). I had my warranty card in hand (2-year-rubber stamped "Dec 2006"). A very nice lady answered the phone (followed the digital menu-got to her on the first try-answered immediately). I explained I needed the 3-speed switch, that the fan was factory installed in my 2007 Damon, and I realized that I was out of warranty. She informed me that it had a 7 year warranty (!?) and I only had to pay shipping ($12.50) on any parts. Who was I to argue?
The down side is they are closed for inventory. Go figure. What genius would close an RV store in Spring? In any case, it will ship next week. I asked for an email confirmation, and was told that I should call back the middle of next week with my order number and she would give me the tracking number. I guess that kind of goes with them not having an online store.
The mystery component remains so. I agree that it can't be a diode, as it would have little use in a DC circuit, not to mention that the fan reverses, it is in series with the motor, and the reversing switch is before the component. If I jumper it, the fan runs normally, all 3 speeds work just fine. I froze it (upside down canned air), but it remains an open circuit. If I figure it out when the new one comes I'll post an update.
Again, thanks for the help. All is well....
We've run out in the house, but the RV has two.
Damon Challenger.
Jeep Unlimited toad