Done some searching but can't find my answer... I'm sure someone on here has done this.
I installed 05 E Fans on my 01 GMC using the 3 relay harness and 2 pins into the computer harness. 1 in PIN 42 and 1 in PIN 33. Everything works great and I'm really happy with this mod.
Now for track use, I would like to put an override switch so I can run the fans whenever I want. Not sure how or where to wire that in. Anyone that has done this, can you post up a pic or info on how to do this. Thanks.

 

Try this

https://www.performancetrucks.net/fo...-truck-542739/

The 3 in the picture in the first post are in addition to the 3 in your main harness. Depending what type of switch you use and if you have the ac sensor installed you could get away with just 1 more instead of 3 more.

 

Ok thanks man, I will look into this a little more this weekend. I do have the ac sensor but my wire harness does not tap into the AC at all. It just has the 2 pins going to the computer. So both fans come on at low speed 190 temp then when it reaches 205 or 210 don't remember were I set it to, both fans go to high speed.

 

If you have the sensor going to the PCM then you can have the PCM control the fans based on AC pressure, so you don't need any additional wires than the two you have already.

 

Sorry man, I'm not following you how the AC Pressure controls matter for an override switch? My fans work perfect right now, I just want to add a switch in the cab for track use only.
Sorry, electrical/wiring is not my strong point.

 

They don't, I was just saying in that diagram I linked to you will only need 1 relay to do what you want, not the 3 pictured. Ignore the other two.

 

You want two diode isolated inputs into the fan relay. This is a common scheme for doing things like the HI/LOW mod.

Some fan harness actually come with this already constructed.

 

That would also work, I just prefer relays to diodes.

 

Oh ok, I think I get it now....Maybe.
So off the manual high relay tab 85 I add another relay before going to the switch?
Or do I just wire in a switch off tab 85 on the manual high relay?
Because I already have the 3 relay harness that kind of looks like it is wired the same way as your diagram.

 

This is the easiest way, but you will never have 1 fan high with the other off operation if that's important to you. You can get around this by using a DPDT switch (and eliminate the relay) that has 3 positions off Low, Off, and High, but this may be more than you need or want.

Ah screw it, I attached that diagram as well.