Alright, this is for any of you guys who know a lot about electrical on a truck. I recently put an electric fan in my truck. I had to replace the fuse holder because it couldn't hold big enough fuses, they kept blowing. So this morning I put the bigger one in, that holds bigger fuses and it worked fine. Started the truck and drove it, worked fine. The fan turned on when it was supposed to, and turned off when I shut the truck off. I have it hooked up so when I turn the ignition off, the fan turns off. But now all of the sudden it wont turn off at all. Even when I have the ignition off and the key out, the fan still runs. It worked great before, but now it just keeps running. The only way I can get it to stop is to take the fuse out. Does anybody know why it would suddenly do that? I'm stumped because I don't know a lot about electrical. Especially since this morning it worked like it was supposed to, but now it won't shut off at all. If anybody has any suggestions, I would appreciate it.

Where is you power source? Do you have some sort of temp switch controlling the fan, or is it on constantly when the key is on? Do you have a relay? You could have gotten your power supply mixed up with a constant hot. A temp switch could be shorted inside, as could a relay, keeping the fan on constantly.

Buy a test light. Check to see where you can tie into an ingnition on power source.

I just have it hooked directly up to the battery for the power source. It does have a relay and it has a temp probe that you put in the radiator. But all I know is that for some reason it works like its supposed to now. Just that little while it was stuck on.

probably fried the relay with the fans huge amp draw @ start up.

I dunno, it works well now.

add some cheese too it...

Make sure that the temp probe is not keeping your fan on after you shut down your engine. With the engine not running it could take quite a while to cool down the engine since there is no flow..

V= I * R

It's supposed to turn off when I turn the ignition off though. And tonight it did the same thing again! So I don't know what's wrong...

Well, if it's not hooked up to an ignition on power source, there's no way it's gonna shut off with the ignition. Seems to me the way you have it wired - powered directly to the battery - it's gonna turn on anytime the radiator temp exceeds the setpoint.

It does have a wire that I hooked up to one of the moduals on my truck that turns off when I turn off the ignition. But for some reason it doesn't always do that.