Trying to hook up a brake controller to the cold wire.
Anyone know which color it is?

No....mine is not prewired.

 

If your controller requires a 12v (battery/charging) voltage, you won’t be able to use the wiring at the brake switch. It’s not a typical on/off switch but a position sensor. It receives only a 5v reference from the BCM and has parallel circuits from the PCM as well. As the pedal is pressed the voltage drops across a resistor (linear potentiometer), so even less voltage is sent from the signal wire.

Even without a blunt cut harness, there should still be taps available in the under hood fuse block to set up a brake controller. Remove the stop lamp relay and jumper pins 30 & 87, then check for power at the taps for fuses 68, 69 & 70 - these are all upfitter and trailer provisions in the fuse block.

 

Well that sucks...thought i had it down!
thanks for the info.

 

Gumby22...can he access any upfitter information online. Dodge/ram provides this, does gm?

 

Again, the most obvious solutions escape me...

https://www.gmupfitter.com/

I’ve only ever been on this website once when I was installing a plow on a customer pickup - one of those things you know but forget!

 

I refer to the upfitter manual A LOT

 

That did it...thank you sir!!!

 

Glad it worked out.

Today, brake controller... tomorrow, the world! Or at least, that abandoned lot across the street!

 

Not the world, but maybe the next issue!!!🤣

Are you an expert on all express items or just brake controllers/electronics?

I'm having a screeching that sounds like a loose belt on my 2020 4500 express. Someone told me there isn't a belt tensioner on the 2020s....is that true?

 

Not an expert - I’m an auto tech by trade and I have several customers that either want brake controllers installed from scratch or have problems with the controllers they already have. I’m constantly referencing wiring diagrams for several different makes (though GM is by far the largest part of our customer base) to diagnose controller and/or trailer wiring problems, so I’m often looking for solutions like tapping into the fuse block instead of the brake switch.

I’m yet to see a 2020 express, but last I knew, the primary drive belt still uses a tensioner. The AC compressor belts (on the trucks and vans at least) have been using a stretch fit belt since at least 2014, so I expect that hasn’t changed.

Try cycling the AC on and off to see if the squeal changes in pitch or goes away. If yes, focus on the AC compressor and belt. If not, remove the primary drive belt and spin the pulleys one at a time to check for noise.