thats making my head spin! haha not really, wiring just intimidates me for some reason. Looks fairly straight forward i guess

 

Wow atomic, thats alot of wiring and stuff i didnt do with mine. I just make mine where they xome on high when temp gets up and come on high when the a/c head pressure gets high.
Charcoal, i didnt get my trans today. Should get it tomorrow then il look at it and send ya a text.

 

It is how the factory harness's are wired up. Its a two-speed setup to be controlled by the PCM or manually by a switch. They both come on low and run in series so they only see 6v, then when they come on high one of the relays throws the system into parallel so both fans see 12v and run at full speed. This kind of setup is very gentle on relays since the current is always shared by at least two of them. Im still using the same cheap relays I got from partsexpress after 3 years.

 

Yes that is the correct schematic for the stock two speed fan wiring. Its really pretty amazing what you can do with normally closed relays hooked in series like that. I actually sat down and drew up a series parallel schematic for the 95s fans which came from a 07 tahoe and it even made my head spin before I got it all figured out. I have one control circuit from the PCM only and currently have the fans wired in series only and it turns the fan on when the temp gets up to 185 and anytime there is an AC request signal. Works fine except the high pressure did get a little high this past summer, around 325 after extended idle but it still blew ice cubes at me. But I drew up a schematic anyway to make it work exactly as it does now only with a A/C trinary switch that would turn the fans on high while still maintaining PCM control and the ability to command the fans off after 40 mph all the while running in high below 40 mph and above 225 psi. My brain hurts just thinking about it but it can be done using only 3 relays.

 

Yep. The above schematic can be used for the PCMs that only have 1 fan output, 99-02 i think. Use the pcm control for the low speed and the AC clutch for the high speed.

 

Its my understanding that a 99 PCM with the 02 operating system will allow you to have two fan controls and for whatever reason the 99 only allows one. I guess the PCMs are physically identical?

 

would you be interested in sending me the info on building the e fan harness. I’m currently converting my 2500hd 6.0l Silverado to efans

 

I've built my own and had pre-made ones. The premade one I bought this time was better than OEM quality and easy to install. I would do that again. You won't save much building it yourself especially after you figure in your time spent on it.

 

You can get all the connector parts from Mouser, and wire from old harnesses. Then all you have to source is some appropriate relays and connectors for those, and fab up some way to mount them

Honestly though, as eeeeeeeeezy as it is to gank all of it down at the local buzzard nest, it doesn't make sense. The factory relay assy just plugs right directly onto your fusebox, almost as though it was meant to (can't imagine why...) and the wiring just fits and all plugs right in, except that you still have to do some work at the main ECM connectors. It's just TOO EEEEEEZY to use the OE stuff, not sure what benefits anything else would even have. Check the writeups in the Technical Write-ups forum on this site, it's all in there.

 

As said above... why build some contraption when the OEM one is scattered across yards everywhere. The factory e fan harness on the gmt800 is the same across the board and it's a stand alone literally taped on the forward lighting harness. Clips right in and off you go... just remember to get the trigger harness out of the computer. It's just 2 pins you push out, green connector 33 and blue connector 42.

It probably made more sense back in 2011 when this thread started to build one as they wouldn't have been in every you pull it yard quite yet...