Thanks, William. I'll try jumping the wires on the thermal switch -- tried that once, but don't recall whether I had the ignition on (think I did). When I jumped the wires I got a clicking sound (chatter?) in the vicinity of the fuse box -- which made me think the problem was probably a relay. Can you tell me which relays control the aux. fan? (don't have a wiring diagram -- purchased a manual for the engine, but no wiring diagram.) These are very helpful responses. I didn't know this was a two-speed fan, for example, and I wasn't sure whether any of the relays in the fuse box belonged to the fan. getting closer, hopefully.