2000 GMC 2500 Trailer Wiring

justinh · March 28, 2005

Hello,

After beating myself all weekend trying to install a new Prodigy brake controller, I'm beginning to believe that I don't have the trailer tow wiring!

I put both a 40amp and 30amp fuse into studs 1 and 2 (actually, the 30amp was there already). I purchased the direct plug to go from the controller to the trailer plug port in the convenience center near the brake pedal. There is no 12v current running to the black wire/post. The only two posts that work are the red (sends 12v when the brake pedal is depressed) and white (neutral).

I stumbled across an article that says these will be the only two posts that are active on a truck without the trailer tow option, and that both the blue (trailer brake) and the black (12v positive constant hot) need to be connected to the battery with an in-line 30amp circuit breaking block, and to the back of the truck for the trailer brakes. I guess these wires terminate in the engine compartment near the vacuum assist???

The 12v lead is pretty straight forward, but the blue lead has me confused. Do I need to run this lead to the back? Isn't the blue wire located in the 7 pole trailer connection (which is on my truck and what lead me to believe I had the trailer option)?

Any help of locating these terminations and what I should do would be greatly appreciated.

Thanks!

Justin

builderpaul · March 29, 2005

Hello,

After beating myself all weekend trying to install a new Prodigy brake controller, I'm beginning to believe that I don't have the trailer tow wiring!

I put both a 40amp and 30amp fuse into studs 1 and 2 (actually, the 30amp was there already). I purchased the direct plug to go from the controller to the trailer plug port in the convenience center near the brake pedal. There is no 12v current running to the black wire/post. The only two posts that work are the red (sends 12v when the brake pedal is depressed) and white (neutral).

I stumbled across an article that says these will be the only two posts that are active on a truck without the trailer tow option, and that both the blue (trailer brake) and the black (12v positive constant hot) need to be connected to the battery with an in-line 30amp circuit breaking block, and to the back of the truck for the trailer brakes. I guess these wires terminate in the engine compartment near the vacuum assist???

The 12v lead is pretty straight forward, but the blue lead has me confused. Do I need to run this lead to the back? Isn't the blue wire located in the 7 pole trailer connection (which is on my truck and what lead me to believe I had the trailer option)?

Any help of locating these terminations and what I should do would be greatly appreciated.

Thanks!

Justin

<{POST_SNAPBACK}>

Z82 is the rpo code for the trailer package. If it is not on the rpo sheet, in the glove box, than your truck doesn't have it.

If it doesn't have it then you will need to splice into the correct wires. The controllers instructions should spell out which ones.

I am not familer with hard wireing the NBS trucks. (mine was plug and play with the z82) I did have to hard wire an OBS. There were 2 wires (Red and Blue) taped under the master cylinder. The blue got spliced into one controller wire. That already runs to the back of the truck and gets hooked to the trailer brakes. The hard part was finding the brake light only wire to splice into.

builderpaul · March 29, 2005

Just realized I am in GM-tech forum. sorry if I was not supposed to relply here. Just so you know I am not a GM tech.

GM-Tech · March 29, 2005

Just realized I am in GM-tech forum. sorry if I was not supposed to relply here. Just so you know I am not a GM tech.

<{POST_SNAPBACK}>

Hey, if you know the answer, and it sounds to me like you gave a pretty good answer, by all means reply!

This forum is not just for me to answer questions. For one thing, I certainly don't know everything. If you have first hand experience with something, please share your knowledge.

At our labor rates, people don't come to us to install trailer wiring, so we have little experience with this sort of thing. I could figure it out, but I'd have to do some research, so you saved me some time.

justinh · March 29, 2005

Got it!!! You're all going to love this.....

First off, I have to give kudos to Brad's Trailer Service webpage:

http://www.bradstrailer.com/generic_wiring.htm

and etrailer for their pictures:

http://www.etrailer.com/faq/cbc.asp

and to all of you on a couple of forums that I emailed direct (you know who you are) :-)

There is a paragraph (second from bottom) that made me realize that I probably don't have the trailer wiring option, even though I had the 7 pole harness in the rear of the truck, the 30amp Maxi fuse in stud #1 under the hood electrical center, and the trailer brake slot in the convenience center near the brake pedal.

There is a sentence in brads trailer page that says for vehicles without the towing wiring option: "...This connector will be available on all models without trailer tow option. However, the only wires that are useable at the connector end will be the stoplight (RED) and ground (WHITE)."

They were nice enough to put me in touch with one of their service techs (I have never purchased anything from them) to help me out. I was told to remove the cover from the electrical center under the hood (just like the pictures on the etrailer website). It was here that I assumed I'd find the terminations from the black 12v convenience center lead, as well as the blue trailer brake lead. Well, not only did I find them, but I also found the red wire termination that runs to the trailer connector to power the trailer battery as well as the blue wire that comes from the rear connector to complete the trailer brake all the way to the rear!!

The funny part....each red lead had a round terminal post ring crimped to the end, one had a small ring, the other had a larger ring....each of these rings fit perfectly over the positive posts located in the electrical center, and the blue wires both had that special GM connector (male and female). Now I wonder why they never connected these when the 2000 and 2001 Sierra's were built??? (My mom's boyfriend's 2001 Sierra had the same symptoms as mine) I thought maybe because they didn't want a positive always live to two locations that may not be used, but they could have just removed the Maxi fuses from Stud #1 and Stud #2!?!?!? I believe these fuses only power the brake controller and the auxillary battery charge. I do remember something about not being able to get the trailer package when you get the plow package, but I just don't get it.

Whew!! I have a Masters Degree in Software Engineering, and I don't think I've ever had to research this hard during that whole process. I now have even MORE respect for guys and gals that get to do this every day for a living. Thank you! ;-)

Sorry for the long post.