I always run a lead from a switched source to activate the fan relays on my cars. It does not take the fans long to drain a battery when you forget to shut them off. Usually the lead that runs the radio is a good choice since it is usually a switched lead, and I am trying to remember if that is true on the Squarebird, been a while since I wired in the radio.

I also like to run a lighted switch so I can glance at it and see if it's on or off.

This diagram is pretty close to how I am running the dual fans in my olds.

That's similar to how I was going to set them up. I will be using an automatic switch later on but I'm more just getting everything setup before I pull the engine back out.
Is the radio wire a constant 12v or a ignition switch 12v.
I'm probably guessing that it's not constant as I'd assume the old radio wouldn't have had memory haha.
That drawing is basically the same as I'd planned on doing, I was just curious about suitable wiring to use.
Thanks Chris.

Should be easy to test, if you can find the lead under the dash for the radio. There isn't a fuse block, just inline fuses if your car is anything like mine.

Run a test light or gauge on the lead and see if it's hot without the key on vs off. Or if your radio works... does it work with the key on or off... My radio is out so that test wouldn't work

Yeah I'll have a look this afternoon. The radio worked and I've cut the wires so it'll be easy to check. I'll also be installing an aftermarket radio so I've kept that wire separate.
Cheers.

The radio lead came switched by the ignition from the factory.

Chris, is your car equipped with A/C? If so, one of the fans MUST come on with the A/C clutch. It is important to keep air moving through the condenser any time the compressor is running. If you don't, pressure will build until the safety valve spews Freon out.

Power your fans from a fused battery lead. Be careful to run the fans in the correct direction (direction can be reversed). Run power to the relays from your key switch (the radio lead is ok). Relay coils take no power to run. Make sure the relay contacts are heavy enough to carry the current to run your fans. - Dave

No air con Dave so all good there. Yeah all pretty straightforward to do.
I will have to swap the wires around to push not pull as I'll need to mount the fans in front of radiator.
I'll run from the relay directly to the battery+ via a 30 amp fuse on each wire with some good size wire so hopefully it will be ok.
Thanks Chris.

#10 AWG copper wire continuously carries 30 amps safely. Having said that, make sure your connections are tight. 30 amps is a lot of power and DC is continuous. A loose 30 amp connection will burn. I use crimp ring terminals with bolts and nuts to get the tightness I want. If I ever need to, I can disassemble the splice by removing the bolt. This is how we do electric motor leads at Ford.

You will remove the fan and spacer which will offer more room for you to shim the radiator towards the engine for more front fan space. I did this on our Galaxie and it works great. - Dave

Ok, that wire size will be easy enough, and yep tight connections.
There's already no fan and the nose of the pulley is very close to the radiator.
As I've got the windsor in there now with a different radiator, clearence is a bit of an issue.

Ok all hooked up and no go. I had lots of clicking under the dashboard but no action. Double checked everything all seems good.
I tried to switch of the radio wire first and now switched off the heater wire.
Checked with test light, got power to the relays but that's where it stops.
Not sure what's going on.

What size alternator are you running? Some of these fans will draw more that the older alternators will put out.

Are your relays under the dash? Also what size relays are you running?

I'd run the relays up by the battery to keep the high power leads as short as possible and run the activator wire from the switch out to the relays. Then you only need the one small lead out from the cab to the relays.

And I would agree with Yadkin, if you aren't running a stout alternator, you may find you are running off battery at idle and low speed and the alternator won't keep up. I'm running a 115 amp gm one wire on my olds with the dual fans to keep up. I started with a 130 amp, but it died and I had a local alternator guru rebuild it. He said the 130 was overkill and wouldn't last long... so I went with his advice. I have a 120 amp powermaster on our 58, but have been fighting it causing the belt to slip.

Just like all relay circuits (power top, power windows, seats, etc.) think of your circuit as two independent circuits. One 'side' is high power (fef from the battery) and the other is control (fed from the dash).

If you hear clicking, that is the relay coil(s) energizing the control side contacts.

The power side simply switches battery power, on and off to your motors.

Start at the fan motors, individually. Connect a long jumper 'test wire' to your battery +. Be careful not to ground this hot jumper but touch it to the motor lead that is not grounded. Does the motor turn? If not, reverse the motor leads and see if it rotates in the other direction. Test both motors.

Simple DC motors should work in either direction but I have found some that the manufacturer put a diode in for one direction only.

If the motors do turn in either direction, follow the motor lead to your relay's normally open contacts. One side of the normally open contact should be hot all the time and the other side is your motor lead. You can use that jumper wire on the relay coil to temporarily energize it, just to bypass the thermostat.

I'm assuming a lot here. I assume your fan motors are properly grounded and so are your relay coils. I also assume you put the fuse close to your battery so as much of the circuit as possible will be protected, and that all connections are tight. - Dave

Ok, the relays are right next to the battery, I'm using 2 30 amp relays. The wire I'm using is suitable for 50 amp, I've checked all connections, they're good. All the earths are solid so I'm happy there.
I'm only trying to get them to operate off a manual toggle switch in the cab at the moment as this is all just test fitting prior to removing engine. So I don't think the alternator is an issue, that will be big enough, 100amp.
I've tried jumping the fans manually but that's not working either so I'm wondering if there might be something wrong with them.
These fans can operate either direction as I've used them on other cars.
So Dave your saying to just jump with a lead straight off the battery+ and connect to the fans without fan earth attached. Which I tried with no luck.
Thanks Chris.