So after reading a few fan switch how to's, it seems like with obd II cars, if you wire up a fan switch, then turn the car off with the fans running, they will keep running.

Is there any way to wire the fan switch so that when the car is turned off with the fans on, the fans will turn off? On my last car (obd I), this is how the switch was wired, so I could keep the fans on low all the time since I mostly drive in traffic anyways, and I wouldn't have to worry about forgetting it on when I turned the car off. Thanks...

 

It's funny. OBD-I people want to have constant power to the fans like the OBD-II cars have, so they can run the fans with the key off. You want the opposite.

You will have to change the fan relay coil power to a switched power source or put a relay on that feed, that will cut off when the key is off. Alternately, you could put a relay on the ground feed of your fan switch that would open the ground when the key is turned off. Those are only a few possibilities.

 

Yea I was told the same thing by my friends when I proposed to them the question.

Seems like the easiest way would be to wire a a relay to the switch somehow. Could you explain more about wiring a relay on the ground feed, how, and why it would work? Thanks!

 

A relay between the switch and wherever you are getting your ground from it is what you would need. The relay coil would be need to be wired to operate when the key is ON. The ground would need to be wired so that it passed through the relay when it is operated. When the key is turned OFF, the unoperated relay would disconnect the ground and the fans could not be turned on by the switch.

 

be a lot easier to get a switch with a light on it. besides that, if you leave it on one time, you wont forget to turn them off the next time.