electric fan diode?

Is there a way to have my electric fans turn on only when the engine is running? Right now I have the relay trigger wire hooked up to a switched 12v at the fuse box. So if I shut off my car when its hot, I cant turn the key back to the on position to listen to the radio without the fans running and draining the battery. Would putting a diode somewhere make it so that this trigger wire would only be hot when the alternator is charging the system (engine running)?

use an oil pressure switch to switch 12v on the relays switching current

The key accessory position is designed for that as long as you don't have the fans triggered from that circuit.

You are feeding a relay hot side of the COIL with a wire off your IGNITION + 12, if it's a HEI, its the same pink wire.....if it's points, just make sure you find the pink wire behind the dashboard, or off you fuse block marked ignition at that fuse...I think there is a tab there you can use....

the main power through the relay comes off the alt output stud directly....

010752 said:

The key accessory position is designed for that as long as you don't have the fans triggered from that circuit.

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Which is the acc. position? Mine is LOCK, OFF, ON, STRAT. Radio is wired to the factory radio 12v+ and ground wires and it can only turn on with the key in the ON position.

mrvette said:

You are feeding a relay hot side of the COIL with a wire off your IGNITION + 12, if it's a HEI, its the same pink wire.....if it's points, just make sure you find the pink wire behind the dashboard, or off you fuse block marked ignition at that fuse...I think there is a tab there you can use....

the main power through the relay comes off the alt output stud directly....

Click to expand...

So you are saying that I should find an open tab that is off with the key in the OFF position, and is only hot with the motor running? I cant read anything labled on my fuse box anymore so ill just get under there with my voltmeter and search for it. Engine running and sidepipes is a burn waiting to happen though... hope I can find this tab quick.
I went back to old school points after my mallory crapped out on me so no HEI here either...
And I have the main power feed to the relay coming from the alt stud with 2 fused 10# wires (dual relay setup).

And TT- I would rather use one of these possibly existing feeds if I can, rather than put in a pressure switch.

I THINK you have to push the key IN and then turn counter clockwise, that goes to the accessory position, ign and so forth is not hot then.....the yellow wire to your wiper motor plug with 3 wires inline on it....that's also a switched hot to/like ign...but it's fused separately...has enough power for a mere relay coil though, not to worry....

in accessory mode, as above by that switch....it should not be hot, then you can run radio and shit without engine being live....as i recall it kills HVAC blower too....

:drink: