Originally Posted by El_Beautor

You need to make sure that you use a relay with a flyback diode built in, or add one to your wiring. If you don't the relay opening and closing will kill the temperature switch with voltage spikes. The flyback diode prevents the voltage spike on the trigger line from the temperature switch and protects it. In case you want to know what a flyback diode is, here's the Wikipedia article on them, and here's an article explaining why they should be used in circuits with relays. There's quite a few people on the S10Forum who have run into the same problems as you describe, and using a flyback diode on the relay solves the issue.

I've been using my cheap $15 Amazon temperature switch for about 8 months now without issue.

Originally Posted by blazen_red_4x4

I hadn't even considered that, good info, thank you!

I've read about it being common practice on momentary switches before, the diode keeps the switch contacts from arcing and causing a buildup of corrosion, which leads to the switch no longer working.

Originally Posted by eshaw

Mr. Electrical I'm not. Is there a how to on this any where? I have a twin Intrepid fan setup mounted to my radiator in my project truck. Eventually I'd like to have the 0411 computer run this setup but until that happens I'd like a cheap way to run the fans without reverting to buying an aftermarket controller setup. Most of the reviews I've read on multiple sites give them less than stellar reviews.

Originally Posted by eshaw

aftermarket controller setup. Most of the reviews I've read on multiple sites give them less than stellar reviews.