# trailer wiring pulg (05 chevy) not working AAAAGGGGGHHHH!



## watcher

I'm at wits end. I went out this morning to do the simplest thing. Hook up the lights on a new to me trailer and see if they work or not. But now I'm ready to run the truck and trailer into the river.

I bought a used Chevy Silverado, it had a receiver and the big round factory installed lighting plug on it. I bought an adapter to allow me to connect the flat 4 prong plug already on the trailer into it. Well I made a stupid assumption, I assumed the factory installed plug would have power to it and work. As you might have guessed by now, it doesn't and I can't figure out why. 

Checked all the fuses I could find and the wires as far as I could reach under the truck. Anyone ever dealt with something like this?

The quick option is to just buy a trailer light kit which would give me the necessary plug but that doesn't fix the problem with the factory installed system. Plus it'd cost me another $20 and a never ending chorus of "why didn't you do that in the first place" from the wife.


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## cfabe

As I recall from doing some work on an 03 or 04 suburban, with the factory 7-pin connector the brake lights should be working from the factory. If you want to use the constant power from the truck you'll need to install a fuse in one of the fuseboxes. The brake wiring comes to a junction box under the dash where you can plug in a harness from a brake controller if you need one.

As for your problem, If I were you I'd start tracing out the wiring. Get some good wiring diagrams and check for the proper signals everyplace you can get to the wire. Eventually you will trace it back to the problem area.


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## Cartman

Have you used a test light to make sure you don't have power to the plug?
Do you have the hitch connected to the truck?
Sometimes the lights will not work because of bad ground to the trailer.
At times the lights on my gooseneck stock trailer don't work until I move it around a little to get a good ground through the hitch. Good luck I know how flustraiting that can be.


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## hunter63

The three things I hate most:
Trailer lights, post hole diggers, proctoscopes, not necessarily in that order.
I share your pain.

Now that we are past that,
Bad ground in either the truck or tailer is the most common cause of trailer light not working or being weird.

Need to find out if you have power at the plug (as was stated) for each function
Check with meter or even a bulb with wire on it, from each pin to *chassis ground*, with:
1) lights on
2) lights off, directionals on, right/left generally tail lights and directionals share the same wire, but you need to see if the plug has power from pin to ground.If they work, but lights don't on trailer, suspect ground.
3) brake lights, have someone push peddle for you.

If no power to pins in plug, check glove box for wiring kit/relays/ wiring diagram.
Might not have been installed.
Check inside the plug itself (if possible) connections might be just corroded.

If these all work, need to check each circuit on trailer lights, including ground.
Good luck.


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## watcher

I guess I didn't make it clear. I *know* there is no power to the plug because I checked it out with a multimeter and it show 0 volts on all the prongs.

I have checked for which fuse or fuses were the trailer wiring in the owner's manual, which is a waste of paper and time.

A bit more info. The truck has a electric brake controller mounted and the little red light on it comes on when I press the brake pedal BUT what the manual says are the factory installed brake control wires are not connected. (remember I bought it used). I have also discovered someone installed one of those round 5(?) prong trailer light plugs, it was hidden under the bed liner. It is attached to the factory wires but it also has no power.

I'm thinking there is a fuse or relay which is either bad or missing but w/o a wiring diagram I'm lost. I hate the idea of having to take the tuck to the dealer just to have them charge me $50 to put a fuse in. I'm going to call the local dealer and see if they will give me some free over the phone help, but I'm not going to hold my breath.


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## cfabe

Okay I did a little more homework for you. On these trucks you can have a 5th wheel trailer wiring provision which sounds like what you have. The 5-prong plug in the bed was installed by someone, onto factory wiring that dead ends there. This runs in parallel with the normal 7-prong plug by the hitch. 

There are three fuses you need to check for the brake lights:

In the underhood fuse block, left(driver) side of engine compartment, for the trailer parking lamps "TRL PARK, 10A fuse, brown wire in harness goes straight to pin F at 7-pin connector. 

In the cab fuse block on the driver side of dash, "RT TRLR ST/TRN" 10A fuse, dark green wire to pin D, and "LT TRLR ST/TRN" 10A fuse, yellow wire to pin G on 7-pin connector. 

The wires for these circuits goes directly from these fuses to the 7-pin on the rear of the truck, with a splice near the 7-pin going up to the 5th wheel provision. You should be able to check for continuity from one of the fuse pins to the trailer connector to determine if a wire has been cut somewhere.

The ground for the trailer connector is a white wire bolted to the spare tire hoist support, the left side of the fuel tank, or the rear body mount, depending what body style the truck is. 

The trailer brake wiring should be a dead end harness under the dash. Red is power for the brakes from STUD 2 fuse in underhood fuse block, 30A fuse. Dark blue is power out to the brakes from the controller, goes to pin C on the 7-pin. Light blue is brake signal from brake pedal. Brown is illumination or parking lamps, black is ground.

The +12 constant for the 7-pin is from fuse STUD 1 in the underhood block, 40A, red wire to pin E at the 7-pin.

Backup lights is Light Green, pin A at the 7-pin.

Hope this helps you troubleshoot your problem.


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## agmantoo

The most common problem that I encounter is that someone wired the trailer without following any accepted wiring routing. Then they just tied the trailer inot the tow vehicle until they got the trailer lights functioning. THEN, when the trailer is connected via an adapter cable the trailer does no match the tow vehicle. Often this will blow a fused on the truck or at best just create a problem as described by the poster. This can be used to trouble shoot your wiring
http://www.accessconnect.com/trailer_wiring_diagram.htm


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## Cabin Fever

You might want to consider forgetting the problem and bypass it all together. Just go out and buy one of those Hoppy Brand T-Connectors that splice right into your tail light wiring system. In my Chevy, I just found the wires that when to the tail lights (back by the rear bumper). In the set of wires, there is a wiring connector that can easily be disconnected. The Hoppy T-Connector just snaps right into this part of the wire set. No cutting of wires! The third end of the T-Connector comes with wires that run to the back of your vehicle with a trailer plug. It takes about 3 minutes to have a brand new trailer plug in.


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## watcher

cfabe said:


> Hope this helps you troubleshoot your problem.


Thank you, thank you, thank you!!!

Between your info and a little sand paper (the contacts were nasty) I got the lights working. 

One of the fuses was blown but didn't look it. I checked all of them with an ohm meter and found it.


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## cfabe

Glad you got it working!


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## watcher

One thing I also discovered. They do not make a lighting adapter for the 05 Chevy 1/2 ton. I can only assume its because they come with the factory wiring installed. If the truck didn't have the factory towing packet the wires were tucked into the frame. Therefore there's just no demand for the product.


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## hunter63

Thanks for letting us know what happened, so many times people ask for advice, but we never hear the resolution.


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