There is a way to do this. Use an oil pressure switch to turn on a relay for the power to the fans. If you have oil pressure, your engine must be turning,no? This is how engines that run on LP gas keep the gas turned on. The switch needed would not be a conventional oil pressure switch; it would be the kind used on industrial engines. It would turn ON at maybe 5 psi.
Maybe another way. Use a time delay relay. These delay the operation for a preset period of time. Some are adjustable, some you set the time with a resistor, some are fixed time. Read up on the TCS system. The 72 delays for 23 seconds. May have a hard time finding a good 72 TCS delay relay, but there are other types out there. I've used them on a LN2 injection system and worked like a champ. Search around.
Yanniz, I read your earlier post and you are having the exact same problem I had with the Windstar fans.
You want to hook up the fans so they won't draw power away from the starter when you start the car. Originally I had mine coming on with the ignition and my car wouldn't start either. The ACC location did the trick for me.
You starter has to be good though if it is marginal than this might not work for you.
Let us know how it turns out.
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