2003 Silverado vs. trailer brake light

Hey all. Have an odd issue hopefully someone will have some insight on...

I have a 2003 1500 Z-71. I discovered that I have no right side trailer brake light. I have 2 trailers (RV & boat) and both have this issue. Turn and hazard work, and both filaments in the bulb are fine...since there is only the two wires for the brake/turn/hazard, it has to be in my truck. I tested with another Silverado and brake lights work fine.

Sooo, I checked all fuses that I could find related to the trailer harness and all are fine. I called my dealer and explained issue, and the mechanic (yes, actual mechanic) told me that the wiring to the harness runs directly from the trucks tail/brake lights. I crawled under there, and no they don't...I was able to trace the bundle from the harness and it goes directly up front. To where I am not certain as it's path goes above gas tank...

I really don't wanna have it serviced, but so far I am at a loss as to what to look at next. Any ideas? Thanks!

Hey all. Have an odd issue hopefully someone will have some insight on...

I have a 2003 1500 Z-71. I discovered that I have no right side trailer brake light. I have 2 trailers (RV & boat) and both have this issue. Turn and hazard work, and both filaments in the bulb are fine...since there is only the two wires for the brake/turn/hazard, it has to be in my truck. I tested with another Silverado and brake lights work fine.

Sooo, I checked all fuses that I could find related to the trailer harness and all are fine. I called my dealer and explained issue, and the mechanic (yes, actual mechanic) told me that the wiring to the harness runs directly from the trucks tail/brake lights. I crawled under there, and no they don't...I was able to trace the bundle from the harness and it goes directly up front. To where I am not certain as it's path goes above gas tank...

I really don't wanna have it serviced, but so far I am at a loss as to what to look at next. Any ideas? Thanks!

under the rear of the vehicle near the spare tire mounted on the underside of the truck bed is a junction block . these usually corrode its a circuit board block. follow the tail lamps/trailer harness wires to this junction. then use meter to find the open / resistance drop.

under the rear of the vehicle near the spare tire mounted on the underside of the truck bed is a junction block . these usually corrode its a circuit board block. follow the tail lamps/trailer harness wires to this junction. then use meter to find the open / resistance drop.

Doesn't connect to the junction. I checked the connections at this point, but didn't test. Either way, the wiring bundle comes from the trailer connector and goes up front without connecting to the junction.

Definitely with j cat on this one. Go with the easiest scenario first and start at the hitch with a tester at the 7-pin connector. Have an assistant press the brakes and test the pins. Then back probe the connector and see what you get. If I understand you correctly, the brake lights work on the truck, but one does not work on the trailer when a trailer is connected. I am still thinking the problem is at the rear hitch. Again, check the block as j cat suggested just to cover all bases.

Doesn't connect to the junction. I checked the connections at this point, but didn't test. Either way, the wiring bundle comes from the trailer connector and goes up front without connecting to the junction.

if that is the case then what this means is your vehicle never had trailer wiring set up from the factory ...

this means we here can not help you. you must find out where SOMEONE hacked into your vehicles wiring ! this is usually done improperly as these connections must be fastened and I solder these connectors so that this never occurs. they may have used those non crimp tool connector/lugs.

GOOD LUCK.

I have already used a volt meter and when the brakes are pressed, no voltage for the right side. But the same pin gets power for 4ways and turn. And yes, I should have mentioned that the lights on truck all work fine.

And no, this is factory. I got her brand new, and this is how it came from GM. I double checked, and indeed the bundle of wires plugs into the back side of the trailer plug and goes up front. As I said, I lose it when it goes on top of the gas tank. Up towards the front, there are at least two bundles so I don't know which one runs to the back....

since the vehicle came with the trailer wiring the junction block that accepts this trailer plug as I explained previously, you have yet to locate.


remove the spare tire , and follow the wires from the trailer plug. only 2-3ft of wire to this block , remove covering and probe for voltage loss with the trailer lights hooked up.

this juntion /connector looking device has diodes in it as well as circuit board. this is a simple device that connects to the main wiring so that this trailer package can be installed . this is all mounted with in 2ft of the rear bumper . all these vehicles have this wiring designed ,,,,,,,so that the trailer wiring can be installed ,,,,,,with no cutting or splicing of the wires.

with this damaged the vehicle lamps will work the trailer light will not.

cost is about 30.oo

Definitely with j cat on this one. Go with the easiest scenario first and start at the hitch with a tester at the 7-pin connector. Have an assistant press the brakes and test the pins. Then back probe the connector and see what you get. If I understand you correctly, the brake lights work on the truck, but one does not work on the trailer when a trailer is connected. I am still thinking the problem is at the rear hitch. Again, check the block as j cat suggested just to cover all bases.

your correct that it is possible the trailer connector is defective. this is another area that has issues..then again owners with very poorly installed wires along with rodents chewing on them causing short circuits that will blow the diodes etc..

My truck did not come with the tow package, so I had to install all of the wiring myself. This was easy because GM included the wiring bundle at the back of the truck, above the spare tire. All I had to do was connect into these and then run an auxiliary power and a brake wire from the fuse center. All of the wiring is in plastic loom, so it is protected. Since yours has the factory tow package, (help me if I am wrong) does the 7-pin connector on the hitch plug into the factory harness? If it does, what does the tester show if you test the wires on the backside of the connector on the harness? If it is not there, then I am at a loss.

Sincerely,
Matt

Thanks for all the replies, i really appreciate the feedback.

Ad for a junction, no. The bundle of wires are connected to the back side of the plug. The bundle run directly to the front, no junction boxes or other connections. Yes, it is factory. I do not know why this setup would be different than your or than is standard, but as I mentioned, I am the only owner and this is definitely from the factory. I do know where the junction you mention is located, but it is not connected to the plug.....

Thanks for all the replies, i really appreciate the feedback.

Ad for a junction, no. The bundle of wires are connected to the back side of the plug. The bundle run directly to the front, no junction boxes or other connections. Yes, it is factory. I do not know why this setup would be different than your or than is standard, but as I mentioned, I am the only owner and this is definitely from the factory. I do know where the junction you mention is located, but it is not connected to the plug.....

what does the vehicle trailer plug look like ? the wires that are connected to this plug what are the colors ?

just to be sure I got this correct /////////the wires going to the trailer vehicle plug run with no other connectors/splices to the front of the vehicle ? correct ?

The reason I asked what this looks like is because I suspect you have the light duty 4 wire/conector. you do not have the 7 pin round heavy duty trailer wiring connector.

this would be the TRL L TURN FUSE OR TRL R TURN FUSE 10AMPS.

not many with this light duty wiring.

once again if you do have this heavy duty round connector , then this being from the factory , will have the T connector , that is very close to the trailer connector , mounted at the rear of the vehicle.

I even checked the exterior wiring schematics and harness layout !

The reason I asked what this looks like is because I suspect you have the light duty 4 wire/conector. you do not have the 7 pin round heavy duty trailer wiring connector.

this would be the TRL L TURN FUSE OR TRL R TURN FUSE 10AMPS.

not many with this light duty wiring.

once again if you do have this heavy duty round connector , then this being from the factory , will have the T connector , that is very close to the trailer connector , mounted at the rear of the vehicle.

I even checked the exterior wiring schematics and harness layout !

Nope. 7 pin heavy duty. Figured pics are worth a thousand words :)

http://i418.photobucket.com/albums/pp267/Kayayem/Posted%20pics/100_3544-1-1.jpg

Pic 1 (top left) is the wiring bundle disconnected from the back side of the plug. I have cleaned all connections on both sides of the plug with connector cleaner.

Pic 2 (top right) is the wiring bundle (where I am pointing) running past the junction. You can see where it runs to the left of the image past my hand and goes to the plug.

Pic 3 (bottom left) is the same from a different angle. I am pointing to the bundle as it runs over the junction and crossmember. Notice the red arrow at the bottom of the image, that is the same bundle heading up front.

Pic 4 (bottom right) is basically same from another angle. The arrows are pointing to the same bundle on each side of the crossmember. To the left side is the rear of truck and the plug. it runs over the junction and keep heading to the front of truck (right of image).

I have no idea why this is different than standard. All i do know for certain is it came this way from GM. Thanks!!

I am happy with your pictures. as you can see you have a junction block 4 connectors plug into it . this is bad . replace this and you are good..........

I checked mine and followed the harness. Though mine did not have the tow package, I believe they still used the same harness and just attached the 7 pin connector end to it. So, with that, the harness does go above the tank and I believe T's into a bigger harness that includes wires from the gas tank, etc. This the appears to go to the fuse center under the hood, where it is fused. If you look at the label on the underside of the cover, you will see abbreviations for trailer (TRL). Check those fuses!!!! Maybe a short on the trailer or something caused one to blow. Again, I don't believe there would be a problem with the wiring, unless it were right there at the hitch. So, the harness should be fine. Let us know what you find.

Sincerely,
Matt

I am happy with your pictures. as you can see you have a junction block 4 connectors plug into it . this is bad . replace this and you are good..........

How is the junction bad? The trailer wiring doesn't connect to it, so that can't possible be the problem... Maybe I misunderstand?

I checked mine and followed the harness. Though mine did not have the tow package, I believe they still used the same harness and just attached the 7 pin connector end to it. So, with that, the harness does go above the tank and I believe T's into a bigger harness that includes wires from the gas tank, etc. This the appears to go to the fuse center under the hood, where it is fused. If you look at the label on the underside of the cover, you will see abbreviations for trailer (TRL). Check those fuses!!!! Maybe a short on the trailer or something caused one to blow. Again, I don't believe there would be a problem with the wiring, unless it were right there at the hitch. So, the harness should be fine. Let us know what you find.

Sincerely,
Matt

The only fuses i found control both turn and break lights. None of the fuses are bad, and the turn signal works. From the fuses to the bulb is the same connection (meaning, there's not a wire for the brake light seperate from the turn signal) the problem must be prior to the fuses. Else-wise, my turn and hazard wouldn't work on that side.

How is the junction bad? The trailer wiring doesn't connect to it, so that can't possible be the problem... Maybe I misunderstand?


remove the tape and plastic coverings

I had a similar problem and it drove me nuts...it turned out the jack at the back of the truck was bad. Didn't look bad...just was.

Looking more into this and thinking about it KaIIen, I follow what you are saying now. Hope I haven't added too much to the confusion. I looked at the wiring diagrams in my Chilton's manual and here's what I see: The trailer left and right also act as the stop lamps. When the brake pedal is depressed, the input from the brake pedal switch, goes through the turn/hazard switch assembly (these are also run through the flasher to the switch and then to each individual wire or both, depending on turn or hazard) then through the electrical center under the hood, through the fuses, to the hitch. From what I can see on the wiring diagram, the left and right are joined together in the switch, but it is separate from the signal lights on the truck side. Draw your conclusions from that. :) As for the tail/brake lights on the truck, of course those are all on a separate circuit. So, what do you think? Sorry if this rambles, as I am on my iPhone and am having a tough time seeing my whole post. I don't see any other connections between signal and brake wires in the wiring diagram. Parking lights are on a separate circuit, and those work fine for you.

Masapell send me your email address. I will give you the details on your park brake question and why this is required this way .