I recently hooked up an electric fan on my 70 Cuda, and I was wondering where to hook the "ignition on" wire. I tried hooking it up to the bulkhead above the Reverse Light hookup, but tonight I ran it and the fan never came on. I hooked up the power source direct to the battery, and the fan turned on right away. Obviously I need to find a more constant, non fused hookup or wire it directly to the battery.

I'm running a 210 dual fan with 35 Bosch Relay and adjustable thermo if that matters. I have the "high" side hooked up direct to the battery with a fuse.

Any suggestions?

The main "high power" side of the relay should be connected to the battery through a fuse or circuit breaker. The "ignition on" wire could come from the +12 volt ignition circuit inside the engine compartment. This is the wire supplying power to the ballast resistor, voltage regulator, and the +12 volt side of the alternator field connection.

Make sure the fans/relay have good grounds also.

If you have an adjustable set up. You can also connect the ignition on wire to a constant on source.

Then the fans will continue to run when the engine is hot and the key is off. It will often cycle after you shut it down.

Make sure your off temperature is higher than your thermostat temp. Run the power wire directly to the battery. Your original wiring harness was never meant to take the load of electric fans.

and i dont like connecting high current devices to the +12v ignition source under the hood. high current fans will drop that 12v to the ignition . grab your 12v somehwere else- another circuit.

If it's run through a relay, the +12V connection will pull the same current regardless of the current draw of the fan/radio/accessory. It's the 'constant on' wire that is pulling the current to run the fan.

sorry, i misread the above post. still, I'd grab my relay control from a different place and not the ign at the ballast

Find a run only 12 volt ignition feed to the relay coil because you do not want the fan to come on during crank on a hot engine.

I ran mine directly from the fuse box. It's a little longer run, but you can choose a circuit that does what you need without breaking existing circuits.

If you have other relays under the hood like for headlights, horn, fuel pump and such group them all together and wire a power source from the alt to a buss bar where you can fuse and pull power. I did this using the fuse box from a late model.

I ran mine to the relays a mentioned but then to a keyed 12 volt source and toggle switch.