I have searched all over and used a test light and have yet to be able to find a wire that is switched on only when the engine is actually running. Looking to find one hopefully around the engine bay fuse box. My only thoughts were that possibly the ignition wires under the dash would be like this, but im not sure if they have power in the on position with the engine off? Does anyone know where I can find a wire like this? Thanks

Edit: Truck is a 97

 

What are you trying to do? The only thing that goes dead when the engine stalls is the fuel pump relay output. It can handle some load, but it has limits.

 

What I am trying to do does not pull much load, Im looking to attach a key tap to it to power the key on line on an efan controller. That way it wont run with the key just in the on position. I tried my fuel pump relay, maybe i should try again but iirc it still had power in the on position.

 

An e-fan consumes MORE energy (& gas) than a mechanical fan, so don't expect it to ever pay for itself unless you do serious off-roading & need to be able to turn it off before fording deep water. A fan controller is a really complex & expensive way to switch the fan on & off - relays are cheaper, more reliable, & more adaptable.

Read these captions:

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I'm not sure about a '97, but the FP relay output is typically DG/Y, and it goes to the inertia switch or the tank select switch.