ok heres what im tring to do. i have a nelson fan harness on my electric fans. it works great all around town and on the highway. when i get to the sand dunes its a different story. it kicks on but not quick enough because as i climb hills there isn't enough air flow for how fast my tires are spinning and how hard im working my engine. last labor day when i was there i couldn't even climb two hill because the truck was overheating.

im looking to jump into the nelson harness and run a toggle switch into the cab so i have control over the fans instead of the computer when im at the dunes.

im looking to run the fans on high as soon as i get into the dunes.


i would like it to turn on and off with the key so i dont forget about it and leave them on.
i would like to try and have the toggle switch just jump into the harness i have so that when its off the nelson harness still works like it always did. but when its on it runs on high all the time no matter what.


can someone please help me out.

also if someone has a wiring diagram for nelsons harness that might help me out in case no one can.

thanks a bunch
Lance

 

Sounds like you got Nelson's harness before he started putting toggles in them. Call him and ask for a wiring diagram with the toggle switch, this way you don't miss anything from here to there.

I'd imagine, only guessing here...you would toggle a negative switch leg to the relay. Essentially over riding the the controls of the pcm's ground switching. But double check with Allen, cuz if it's a positive switch leg from the pcm, that would suck. I doubt it though, most everything these days switches the ground (relay coil speaking)

 

i bought me a two prong 50amp toggle switch. ran one to a ground and the other one to the blue wire on the harness that goes into pin 42. like this i can turn them on when the engine is running or when it is off. (both fans on low)

 

perfect...i knew it had to be something easy.

 

what does the toggle switch from allens harness do?


thanks for the info

 

ok ive been thinking about this while i was ooking under the hood of my truck.

what if i take and bridge into the two fans powers and grounds. run the ground to the ground then run the power to a switch then a relay that is hooked up to a acc wire. would there be any power backing up into the nelson harness if i ran it like this?


here is a little diagram.

 

Since you have the Nelson Harness I think all you have to do is tap into the blue pin 42 wire that goes to your relays. With that wire run it into your cab, connect the switch, then connect one more wire to the switch and ground it. I'm pretty sure that is all you'll have to do.

The blue pin 42 just completes a ground and kicks on your relays to your fans. The power to the relays are always hot when your key is on, the PCM sends the signal (ground) out the blue pin 42, and then the relays kick on your fans.

 

That only turns the fans on low though. He asked for them to come on high. To do that you need a switch, a pair of relays, and a diode. The switch will be used to energize the two relays, one of which connects blue 42 to ground, and one which provides +12v to the a/c wire. Then you need the diode to go between where you tap into the a/c trigger wire and the actual a/c wire in the truck's harness to keep from turning on the a/c compressor when you turn the fans on. I had mine wired like this awhile back and it worked fine.

 

This will do exactly what you want it to

 

Here's a diagram for the electrically challenged. I actually think you can get away with using only one relay if you hook it up this way. Someone double-check everything for me.