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Trailer Backup Lights - Wiring not Working

dhcomp

dhcomp

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Ok, So we're talking about the 2003 Duramax suburban i just got.

No power to trailer backup light circuit (center pin).

Tore into the trailer wiring, regrounded the ground, checked out the light distribution block, all clean.

Checked fuses, all good.

There is a specific trailer backup light fuse, and its good, but neither terminal has power when in reverse. Feeling like this is probably my issue.

Any idea wtf would cause this, without tracing wires up stream of the underhood fuse box?
 
Darren, I hate to be the bearer of bad news, but if you work on enough different trailer plugs, eventually you will learn a bitter truth:

No matter how many pins, or who wired it, the only pins you can have any confidence are hooked up, are: Tail lights, left turn/brake and right turn/brake.

Even a ground is not always there. Beyond that, its a crapshoot. The only time I have ever heard of the backup lights being hooked up, is when you have a surge brake system on a boat trailer, and there is a bypass solenoid on the master cylinder that diverts the fluid back to the MC when you are backing the boat up.

Both my father's and my bass boats had that. I made sure I hooked up the backup lights when I installed my 7 pin Bargman connection. My father's truck had a factory connector, and I had to add the backup lights to it.
They were not hooked up at the factory.

It may be normal for your make and model to have that pin hooked up, but I would not bet on it unless it just quit working, or you know other trucks like that with it hooked up from the factory.

If all else fails, cut the wire from the harness, leaving enough slack from the connector, and run a wire from the backup light wire in the rear light harness.

Of course, it would be best to fix what you have if its actually hooked up.
 
Oh, and that center pin is actually not a backup light per se. Its officially an "auxiliary" connector. Here is the "official" 7 pin Bargman diagram.


7wayconnectordiagram_zps5f1ec75e.jpg


Its the way I wire all mine unless there is a special request.

7wayconnectordiagram_zps5f1ec75e.jpg
 
dhcomp said:
Ok, So we're talking about the 2003 Duramax suburban i just got.

No power to trailer backup light circuit (center pin).

Tore into the trailer wiring, regrounded the ground, checked out the light distribution block, all clean.

Checked fuses, all good.

There is a specific trailer backup light fuse, and its good, but neither terminal has power when in reverse. Feeling like this is probably my issue.

Any idea wtf would cause this, without tracing wires up stream of the underhood fuse box?
Click to expand...


The diagram is pretty simple. May have to pull the fuse box and check the terminals, may have a broken wire. Fortunately the under hood fuse box comes apart easily.

burb diagram.gif
 
Thanks for the responses guys.

I'm worried about it for surge brake release. Thats all I really tow.

I agree that often they are hooked up different, but the body harness on this truck is untouched, there is a trailer backup light fuse, AND its marked on the connector.

Knowing i'm putting a new vehicle side trailer plug on next week, I came up with the same idea you did. Spliced into the tail light, ran it straight to the plug with a fuse.

Really, this is how i hooked it up on my last truck, as there wasn't any trailer backup circuit, and it was fine for years.

That wiring diagram looks really good, i must have a broken wire in the top right box. As much as the body wiring is unmolested, I can't say the same for the under hood, due to the motor swap.

Thanks guys!
 
One other thing, since you are using it to release the surge brakes. We ran those two bass boats for many years.
After the first couple of years, that release system started to become problematic.
Sometimes it was a bad connection with the plug, once or twice the solenoid had issues, and other things.
More than once, I had to stop while backing the boat to the water and tinker with the brakes.

One day, I was at the place we stored our boats, and I was watching them move boat and trailers around with an old 801 Ford tractor.
They were backing my father's boat out of the cleanup area. I noticed that they did not have the light harness hooked up.

I went over to see how they were doing it. There are two arms from the hitch to the MC.
There is a space between the arms and the MC. All they did was slide a bolt in that space, and it stopped the hitch from sliding back and stopped the brakes from locking up when you backed up.

We never worried about the bypass system again. Just made a place on the trailer for a big bolt to reside.
When we got to the boat ramp, part of the procedure for getting ready for launching, along with unhooking the strap and putting in the plug was sliding that bolt into place.

Every so often, one of us would forget to take the bolt out when we started home, but the first time we stopped it was obvious.

Check your trailer. I'll bet there is a place for a blocking bolt on yours too. I know that you want things to work like they are supposed to, but trust me, eliminating any frustration on a boating system is nice.
There are enough of them that cannot be eliminated.
 
Thanks for the tip.

Yep, there is a slide area you an lock out. I have the little silly lockout tools, that i strap on with velcro. There is another dealer only tool that clips over the top.

I have those for backup, but would much rather it all work properly.

Thanks!
 
I thought there is a wire taped up under the master cylinder that needs to be connected to the fuse box? I remember something about this on my 2003 2500HD, the dealership that sold me the 26' box trailer did the fix for me.
 
The 7 wire spade vs. 7 wire round pins are different. On my 04' Yukon XL, my center pin is the reverse (I believe). I also installed a 7 pin spade onto the Blazer.

Definitely need the backup signal to move our boat trailer. Otherwise, it locks up the tires and you can't back it up without just skidding the tires!

qu363_2_800.jpg
 
skunked said:
I thought there is a wire taped up under the master cylinder that needs to be connected to the fuse box? I remember something about this on my 2003 2500HD, the dealership that sold me the 26' box trailer did the fix for me.
Click to expand...


This is the info I need!! Any more details on this?
 
skunked said:
It's something like mentioned below, again it's hard to remember because it was over 10 years ago. I just remember a power wire had to be hooked up and a fuse had to be added that was in an open spot in the fuse box. In fact the fuse was provided by GM and left in the glovebox for this purpose.

http://www.silveradosierra.com/how-...nt-12v-power-for-7pin-trailer-plug-t1712.html
Click to expand...

Thats what mine sounds like. Fuse is there, pins are there, no power to either.
I'll read up on it.
 
I'm a bit confused, cause that link explains adding power to the 12v hot at the trailer.

I need the backup light power, not 12v hot
 
Light green wire is center backup. Goes to connector on drivers side just under tail light. Then goes up to tail light.
 
jeff in co said:
Light green wire is center backup. Goes to connector on drivers side just under tail light. Then goes up to tail light.
Click to expand...

Yep. But on this truck, the trailer harness is fed from the fusebox under the hood, so all the trailer wiring can be fused separate from the taillights.

And that is where my green wire isn't getting power.

My fix was to wiring it like you are describing. Not as "Safe" and "fused" as factory, but worked forever in my last truck. It will work for a while.

Thanks!
 
Although I didn't trace the wire up front (had to install shocks), it sure looked like it went up to tail light...but I guess it could be just a jog and then run up front. Yours may be different for it coming from a Dmax truck but mine is factory for the suburban/Yukon XL. 2500 with 8.1L so meant for towing from factory.

On the Blazer I just tapped into the tail lamp backup wire. Works but I don't tow too much with the blazer due to short wheelbase.

As a side note, I just replaced my auto-ride shocks with Bilstein 5100.....rides just a bit better, so happy. Certainly not worse and 1/4 of the cost!
 
This was a 6.0l Burb before the dmax was crammed in.

The harness definitely splits to taillight, but I traced and tested all the wires at the rear distribution block. Trailer harness definitely comes from a home run to the fuse box.

Works for now, hopefully I figure out why the feed to the fusebox is dead
 
I'll look up the gm schematic for this when I get back to work and see what it shows
 
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