Aux Fan

[DTrain]

Looking for some advice...

Truck in question is a ‘99 K3500. Truck was originally a factory 350 small block truck. I put a 454 big block in it about a year and a half ago. Got everything done and was pretty smooth all in all.

The one remaining piece and one I’ve been delaying on is the auxiliary cooling fan that sits behind the grill in front of the condenser. This is a factory item on the big block trucks, but not the small block trucks.

I grabbed a new fan and what I thought was a factory harness, but it’s just an after market birds nest of wiring. I installed the fan and it had factory wholes and mounted right up where it needed to go. This got me wondering if maybe the factory provided wiring for this somewhere? Seeing if anyone knows and if so where it may be located?

I’m awful with the kind of wiring the kit would require, but do ok if there are some sort of provisions already there for a starting point. Any advice would be great.

Thanks.

 

[alpinecrick]

MaxExpress mentioned in another thread the ECU for the 7.4's have the provision to run the auxiliary fan, did you install a 7.4 ECU?

This MIGHT be the wiring harness you're looking for.
https://www.rockauto.com/en/moreinfo.php?pk=4664736&cc=1303681&jsn=32262

I'm thinking about doing the same thing myself for my K1500's with the 5.7. I'm just wondering where the best place for the probe is.......

 

[TheAutumnWind]

You could just have a relay trigger off of the a/c compressor and/or a thermo switch.

 

[Pinger]

.

The one remaining piece and one I’ve been delaying on is the auxiliary cooling fan that sits behind the grill in front of the condenser. This is a factory item on the big block trucks, but not the small block trucks.

.

Are you using 'truck' there to differentiate from SUV?
My (1999) C2500 350 Suburban has the fan - maybe because of the duplicated AC (front and rear)?

 

[RDF1]

I added a trans cooler fan to the K3500 on the farm and just wired it and the AUX fan to the running lights. So when they go out in the field to haul hay just turn the running lights on and keeps everything decently cool. And it was very easy to do.

 

[SAATR]

The only ECM wiring for the AUX fan appears to be a dark blue wire on ECM connector C4 (Black) pin 6 or C4 (Black) pin 9 depending on 96/97 or 98/99 ECM. It provides ground signal to activate the aux fan relay. The ECM connector socket is empty on my 98, but if you pin that socket and test for ground, you'll know if the factory aux pin output is functional or not. If it is, use it. Otherwise, use the alternatives that others recommend.

 

[HotWheelsBurban]

Are you using 'truck' there to differentiate from SUV?
My (1999) C2500 350 Suburban has the fan - maybe because of the duplicated AC (front and rear)?

I think it's a 2500 series thing. My Burbs have dual ac and heat neither one has this auxiliary fan. But I've seen on here that many of the 2500 and 3500 series got it. May have been optional on all trucks and SUVs, don't know. I'm sure someone on here will correct my presumption....one of y'all with a factory order book, chime in......

 

[Zx1000hd]

I have a 92 C2500 my 454 has two temp sensor and one temp switch one in each head.

The passenger side head is the temp switch side. It runs to a relay on the driver's side fender just before the hood hinge. To power the aux fan over 220° which is on most of the time because those BB are just hot..

Hope that helps

 

[Godholio]

I think it's a 2500 series thing. My Burbs have dual ac and heat neither one has this auxiliary fan. But I've seen on here that many of the 2500 and 3500 series got it. May have been optional on all trucks and SUVs, don't know. I'm sure someone on here will correct my presumption....one of y'all with a factory order book, chime in......

I thought I remembered reading it in the dealer book, but I can't find where it's written. My K2500 Burb has dual AC/heat and the aux fan.

 

[DTrain]

Well I ended up for the short term tying the fan into the parking lights. Works for now until I figure out a permanent switched setup.