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Discussion Starter · #1 ·
What I'd like to do is switch a circuit (via relay) based on whether the engine is actually running, rather than the key position. I can think of some in-depth ways to do this, but I'd prefer a nice simple solution. Is there possibly an existing output somewhere indicating the engine is turning, (or alternator has output, since that's really the condition I want) that I could just tap into?
 

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You could try to tap a relay off the power to the fuel pump, after the FPDM, but be aware that's a variable voltage output so you would need a relay that acts appropriately. You'll have power at key on prime, cranking, and while running. Otherwise, key on and switched will have no power on that circuit.
 

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Discussion Starter · #3 ·
Ideally, I want it on only when the alternator is turning; I'm looking at options for the fans, and I have a habit of shutting off the engine then turning the key back so I can still roll the windows up/down when I'm at Sonic or similar, so I'd rather not accidentally leave them running for 15-30 minutes with no charging and the radio up where I can't hear them.
 

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Ideally, I want it on only when the alternator is turning; I'm looking at options for the fans, and I have a habit of shutting off the engine then turning the key back so I can still roll the windows up/down when I'm at Sonic or similar, so I'd rather not accidentally leave them running for 15-30 minutes with no charging and the radio up where I can't hear them.
Hmm - If you have the shop manual, you could see if there is a free circuit in the fuse box that is powered only KOER, and not KOEO.

If you did try to adapt something from the fuel pump circuit, your specific concern won't be an issue if you tap after the FPDM. If the engine isn't running, the fuel pump will only come on for 1-2 seconds and then stay off until the ECU sees cranking rpm on the crank sensor.
 
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