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12 Volt Trailer Connection Not Working

amlumber

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amlumber Enthusiast

amlumber

Posted
Posted

Getting ready for a trip and I hooked up the trailer, and no 12v DC.

 

I used my volt ohm meter and have no power off the connection on the truck.

 

Can someone help me correct this problem?

dlewis1111 Senior Enthusiast

dlewis1111

Posted
Posted
Getting ready for a trip and I hooked up the trailer, and no 12v DC.

 

I used my volt ohm meter and have no power off the connection on the truck.

 

Can someone help me correct this problem?

 

Which body style do you have? On the GMT 900 you have to connect a wire that is next to the underhood fuse panel on the left fenderwell in order to get the 12v power to the plug. It is already there next to the box, you just have to uncurl it and hook it to one of the terminals on the front of the box. There are 2 of them, one for the 12v power, and the other for a trailer brake system. I am out of the country, and dont remember which one so either check the owners manual or someone chime in here to help.

pwall Senior Enthusiast

pwall

Posted
Posted

Have you had power before ?

Have you check the fuse under the hood? Is the wire connected under the hood that will deliver the 12v to the trailer plug (as in this diagram....not mine so I take no credit for it).

IMAGE REMOVED DUE TO INCORRECT LABELLING!

seamonster Enthusiast

seamonster

Posted
Posted

They didnt come hooked up from the factory, I had to connect the wires under the hood.

The wires are run just need to be connected to the terminals at the fuse block under the hood.

They will be taped up a few inches from the fuse block. I also had to add the fuse, it was an

empy spot. I dont know why they did it this way????? I have the max trailer pkg so one would

think they would connect it but they didnt. Hope this helps!

jerseydrew Enthusiast

jerseydrew

Posted
Posted

from my understanding the one you guys are referring to is the brake controller wire. i though i had seen many posts refer to the wire loomed up by the steering in the engine bay as the wire for the trailer power.

 

just follow them and see which goes under the truck and which goes to the cab. the one that goes to the cab is for the trailer brake controller.

amlumber Enthusiast

amlumber

Posted
  • Author
Posted

I connected that wire 12 v rear after market wire to stud 1 and checked for voltage there, and it is good. check at the trailer connection still nothing. now what am I missing?

 

WTF GM 2 seconds to connect that wire.

 

 

Oh and thank you all for responding so quickly.

Bluedog Enthusiast

Bluedog

Posted
Posted

If you have the new body style:

 

You need to hook up the one that is coiled up under the master cylinder.

 

Go here: 12 V instuctions

 

The picture above is not correct... the wires identified as "trailer battery" are actually used if you have an aftermarket brake controller.

 

If you have the old body style, there is a red dummy fuse that needs to be replaced in the under hood fuse block. It feeds "Stud 1" and is a 40A IIRC.

 

 

 

HTH

seamonster Enthusiast

seamonster

Posted
Posted

I am trying to remember 3 years ago when I did this, I think there are 2 wires, if you look at the picture in the other post.

there is a break wire connected to #1 and the trailer battery wire is cirlced off to the right. I think that also needs to be

connected. To stud #2 maybe?

amlumber Enthusiast

amlumber

Posted
  • Author
Posted

Thank you all!

The wire was the one under the master cylinder. Connected that to stud 2, installed the fuse into spot 70.

My last question is what size nuts do I need to hold down the wires on stud 1 and stud 2 (they are different sizes).

jerseydrew Enthusiast

jerseydrew

Posted
Posted

the trailer battery is supposed to connect to the stud on the right side (if both wires were connected they would be crossed. and that would be an m6 nut for the trailer battery and an m8 for the trailer brake controller. if you are not wiring in the controller then do no hook up the wire as they are blunt cut under the dash and should not be live just hanging there.

rockcrusherrevived Enthusiast

rockcrusherrevived

Posted
Posted
Thank you all!

The wire was the one under the master cylinder. Connected that to stud 2, installed the fuse into spot 70.

My last question is what size nuts do I need to hold down the wires on stud 1 and stud 2 (they are different sizes).

 

if i remember correctly 8mm and 6mm

pwall Senior Enthusiast

pwall

Posted
Posted
<snip>....The picture above is not correct... the wires identified as "trailer battery" are actually used if you have an aftermarket brake controller. </snip>

Thanks for highlighting! Note sure where I got that image. I've removed it as not to cause confusion.

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