[lust4speed]

All I've ever used on my Taurus fan setup are inexpensive ebay 30/40 amp relays. I bought a pack of a dozen relays with the connectors and used them throughout the drag car to run everything. The fan itself has one relay for low and two in tandem for high range, and has never given me any problems. I set it up before the custom relays were on the market (or at least before I knew about them), and they have survived fine. I do have a temp control, but it drives through the relays - I'd rather buy a new $2.50 relay than a $40 temp control unit. As a side note, the thermostatic control unit has nothing more than one 30/40 relay built in from the factory. To be fair, it might have been designed for a smaller aftermarket fan; but the package didn't list any warnings on larger fans. Anyway, it is just triggering the low speed cheap relay so it should never give any problem.

Has anyone traced down the stock Ford circuit to see what amperage relays they used to control the fans? Might be interesting. As far as alternators go, I used a stock 10SI 63 amp for years. With it working pretty hard all the time the case got hotter than I really liked, but it never did give out. I've since went to the new open frame GM alternator with the big bearings, and it runs cool. Not a bad choice at all, since replacements are available at any auto parts store - which is nice if you are miles away from home and "need it now". They are also becoming very plentiful in junkyards for cheap.

Also, I've read that dual relays won't work because one always closes the circuit before the other, but they seem to work fine sharing the load.