i have a nelson harness for my lt1 fans, i want to hook up a switch to turn on my fans manually, say wen im sittin at the track or in traffic for a little extra cooling, how do i do it?!

 

you can connect a wire to the same terminal on the relay that the pcm connects to. The PCM grounds that terminal to turn on the fans, so that's exactly what you're gonna do. When you turn your switch on, it should be grounded and thats all you need to do.

 

I did something similiar...but w/ the option to turn off manually on a 3 position switch...that way if I'm playing in some mud my fan doesnt spray mud all over the motor.

 

u mean splice the blue wire? and put a switch on it, with the ability to ground the switch?

 

exactly, but I wouldn't splice it. I dont really like those inline splices that cut the insulation. I would connect the wire where the blue is connected to the relay.

 

well i did that, i spliced it, threw a switch inbetween with a ground and it didnt do anything.

 

The PCM grounds pin 42 (thin blu wire of Nelson harness). If you tap into that wire and provide a good ground, the fans should come on (I believe that the engine must be running though, or at least key on). If not, there must be an open connection, bad switch, or bad ground.

 

It does work, that's how mine is set up. Check the things bud mentioned.

 

how would you wire it to make both fans come on high? when pin 42 grounds it only puts one fan on low. how would you go about getting both fans on high?

 

Maybe a DPDT (double-pole double-throw) switch that grounds pin 42 and provides 12v to the ac lead would work??