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How to Hook Up the Constant 12v Power for 7pin Trailer Plug

153K views 41 replies 32 participants last post by  s10blazed 
#1 ·
I just purchased a product called White Night. They are rear facing lights that mount over the trailer hitch which plug into the factory 7 pin connector. While installing this I found out that from the factory the 7pin connector does not have the constant 12v connected. This is often used for trailers that would have lights inside or other accessories. This "How To" will show you were this wire is located and what is needed to get power to the 7pin connector.

Open the hood of the truck and locate the wire under the master brake cylinder. It will be sticking out and taped up up with electrical tape. Remove the tape and pull the wire free.


Once the wire is free connect it to the black post on the front of the fuse box. The black post is for the auxiliary power, the silver one is used for hooking up electric brakes for a trailer.


Use a nut to secure the connection


You will also have to get a 40 amp fuse for the number 68 slot to allow power to the wire you just connected.


And now a pic of the lights installed and working.


 
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#8 ·
CHEBBY said:
So the plug for the White Night piggybacks into the factory plug?

chebby
Yup. It comes with another harness that you can tap into the stock wiring but I liked the idea of not having to splice anything. Plus if I want to it takes 2 minutes and I can completely remove the lights and it looks stock again.

*one thing to note, the wiring harness I used is something I ordered in addition to the lights, I believe it is like $15 bucks but well worth it.

Aridium said:
Thats an awesome how to. I literally just ordered one because I saw how you hooked it up :)
Awesome! Glad it helped someone. You won't be disappointed with it.
 
#12 ·
To add another bit of info, those two connections use different size metric nuts, 6mm & 8mm if I remember correctly.

I tow a RV so I have the brake power hooked up all the time. However I have not hooked up the constant 12V to the trailer plug. I did put a nut on the post and fuse in the fuse box but there is a wire bunde hold down nearby that has a clip on it. I untaped the constant 12V feed line from its storage point under the brake booster and stuck it in that clip. This way I can hook it up in a minute or two if needed but don't run the risk of killing the battery otherwise.
 
#13 ·
toadman said:
Very helpfull information. One would think that a truck that comes with a towing package would be all set to go. Not the case with mine and the dealer didn't provide much information. Once again, a job well done with good pictures and good instructions.
aksierra11 said:
Not a problem. I was shocked it wasn't hooked up from the factory either, especially considering I payed for the max trailering package.
My original quote was deleted by Austin.. dunno why..

Bigredchev said:
Just a little added info. The wire for the trailer brakes is between the fender and the fuse box taped up like the b+ wire for the 7 pin plug. It attaches to the other post on the front of the fuse box, and will also need a fuse.
Good info. I found that wire first and took me a few to realize it was the wrong one.

BuxCamper said:
To add another bit of info, those two connections use different size metric nuts, 6mm & 8mm if I remember correctly.

I tow a RV so I have the brake power hooked up all the time. However I have not hooked up the constant 12V to the trailer plug. I did put a nut on the post and fuse in the fuse box but there is a wire bunde hold down nearby that has a clip on it. I untaped the constant 12V feed line from its storage point under the brake booster and stuck it in that clip. This way I can hook it up in a minute or two if needed but don't run the risk of killing the battery otherwise.
Also great info. I had to dig through my spare nuts and bolts bin till I was able to find the right size nut.
 
#14 ·
Has anyone noticed how small the power wire is? Seems like a very light gage for a 40 amp fuse. I wonder if it will actually charge a trailer battery. I've got just 1,000 miles on my new truck, so I won't know until spring, when I get the trailer out. I hope it will be OK.
 
#18 ·
double_d99 said:
hi, followed your advice but got a question. i have the built in trailer brake and that wire is not hooked up that's between the fender and the fuse box and my trailer brakes work just fine. what is the point of the wire?
Not positive as I don't have trailer brake module installed on my truck but it could be for certain types of trailers it pulls power from a different source. That question may take a GM tech or something with a little more knowledge to answer for ya.
 
#19 ·
There is a note in the manual I think that says the built in brake controller gets its power from a different point in the wiring harness than the user installed one.
 
#20 · (Edited by Moderator)
I have the factory trailer brake controller, and it is hooked from a different wire... I hooked the 12V feed with the wire on the left side of the fuse box and I still have a wire on the right hand side (between fender and fuse box) that is not used.

DSCF0535.JPG


DSCF0539.JPG


On the second pic, you can see the 2 wires connected and at the right of the fuse box, the other wire is still there.
 

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#22 ·
aksierra11 said:
CHEBBY said:
So the plug for the White Night piggybacks into the factory plug?

chebby
Yup. It comes with another harness that you can tap into the stock wiring but I liked the idea of not having to splice anything. Plus if I want to it takes 2 minutes and I can completely remove the lights and it looks stock again.

*one thing to note, the wiring harness I used is something I ordered in addition to the lights, I believe it is like $15 bucks but well worth it.

Do you have a part # or despriction of the other harness? Maybe a link? Thanks. I dont like splicing stock wiring either.
 
#23 ·
ive read over this whole thread thus far, Ive read you need a 40 amp fuse for slot #68. What is the fuse size and other slot location #?
 
#24 ·
I have a question...if the 'silver post' is for the trailer brakes...don't you need a 3rd party brake controller? If so, where is the other end of that wire so that you can hook up the power from the silver post into your brake controller? Or am I missing something here?
 
#25 ·
To help others with "older" trucks or with different options. Here's a link to a thread that had some of the same questions, but different answers. Link: SS.com

This thread also has pictures to help locate a "Dummy Plug" labeled B+ in the under hood fuse box.. Pictures are worth a 1000 words... This dummy plug may be the answer to get power where you need it.

Thanks to the original OP for this How to... All good stuff...

:D
 
#26 ·
Here I go again posting to an older thread. :D

But after a long break, looks like tailgating for USF/Bucs games is back on our plate this year. Really digging the new truck and the idea of running a small inverter off the trailer harness to run a radio while we're goofing off before the game. Yeah, I know, I could just get a battery powered radio and keep it simple - but where's the fun in that?

So big, delayed thanks for the writeup on how to provide 12V constant power to the hitch harness. Found the red wire tucked under the master cylinder with no problems; scrounged around in the coffee can full of stray nuts and got it hooked up to the black post with no issues. Of course I don't have any 40 Amp fuses on hand but I'll swing out at lunch tomorrow and fix that . . .

Once that's taken care of I'll post a minor update on the outcome.
 
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