well i got a set and need to know how to hook them up so they will come on when needed instead of running all the time if hooked to a toggle. 2000 silverado, 5.3.

 

Pin 42 on the blue PCM connector is the fan trigger. When it switches, it grounds the wire. You have to have fans enabled in your tune before you can use that pin.

 

are the fans supposed to blow forwards on the radiator or back towards the motor?

 

towards the motor, they suck , not blow.

 

Suckers...

Here is a wiring shematic we used a while back to wire the efans on my brother's 99 Sierra. Link and here is where we connected the ignition source and a/c wires. Link (click on pic)

Here is the complete thread.Link