Hi, I have a fairmont el and need a wire in the cabin or the boot that gives 12v power only when the engine is running. I have only been able to find ones that come on with the acc and the engine, however it is for a fridge I am installing in the car that I only want on when the engine is running as to save the battery.

Any help would be awesome, thank you!

You very rarely ever have the key on without the engine running anyway... That's a sure fire way to flatten the battery... So I'd use an on wire... Not accy...

If you really want a wire that powers while engine is running Then you do have the fuel pump... Although I'd leave it alone where possible...

Other option is you pick up of the alternator light... To prevent upsetting the light I'd use the wire to drive a transistor and then feed that into a relay to switch power to your fridge...

When the engine is running there will be about 11 or 12 volts on this wire while the other side of the globe will have your 13.8Volts...

Cheers,
Tim

Alternatively you know those jump packs? (or make your own out of a 40 or 60AH battery...

Use the on wire to switch a relay which links the batteries together... So when the car is running it charges both... When the key is off the relay opens and the positive link between both batteries is broken...

Then just hook your fridge to the second battery... Then it runs with the car running or with the car off and if it flattens that battery it has no take at all on how the car starts...

This is the system I have, mainly for my winch on my trailer... See my build thread linked in my sig and find it contents page... It is my own made tipper trailer...

I have a 39AH pack in the boot and I turn the car off and then the battery packs separate and then I use the second pack in the boot to run the winch...

Running the winch on the main battery with the car idling dropped the voltage too far and could've upset the electronics so I didn't want to do that... As a side it also makes a good pack to run the fridge off on holidays... Lasts for hours if I'm parked somewhere or out visiting...

Cheers,
Tim

I agree with TimmyA, at least it has its own dedicated circuit and you prevent high current loads on the cars wiring, I did the same thing on my old LandCruiser, as I was sick and tired of replacing fuses.