Today I was wiring up my cooling fans. I was going to hook one up to the ignition so it would run whenever the key was on (like I have done a million times before). I spliced it into the fuse box and everything works fine except that when I turn the car off the engine keeps running until the cooling fan stops spinning. I took the distributor power wire and put a test light on it. When the fan is running and the key gets turned off the power to the distributor slowly dims out (takes like 4-5 seconds) as the fan motor stops spinning.

The fan is directly hooked up, It goes through no relay or anything. I tried hooking the fan up to other places in the fuse box but no matter where I hook it up to the car does the same thing. I have the fuel pump hooked up basically the same way and it works fine. I even tried unplugging the fuel pump just to see if maybe I was overloading the ignition system or something by running too many things, it didn't help.

Any ideas what is going on here? I'm completely lost on this one.

 

It sounds like the fan motor is acting as a generator when the ignition is turned off and the current it produces is not isolated from your ignition by the ignition switch, which it should. You have to isolate it from the ignition or continue to impress your friends.

 

I really don't understand how it could be doing this though. The fuse box should just be supplying it power, not letting it give power, right? I really hate electric. I have no idea where to even begin looking for the problem at.

 

The motor is acting as a generator when you shut off the motor. Their is no switch to isolate it so it sends current back to the fuse box that it is making. The fuse box simply routes it to whatever wants it or will take it at that voltage and amperage, which decreases as the fan slows down and then stops. You have to have a relay or switch that opens when the ignition switch is turned off so that this can't happen. Their is another way to do it, but I'm talking theoretically since I've never tried it. If you put a diode in line with the fan then it should stop this by stopping the reverse current flow.