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My '04.5 Silverado 3500 has been giving me problems for awhile, and I need some help figuring out what's wrong with the system.

On 3 different trailers, I'm getting no right brake or signal light, although the running lights are all working, including the right side. I'm getting power at the truck plug, using a test tool with led's for each function, which shows the right signal light and brake light are sending power to those lights. Except for the "back up" light not coming on (not a problem since none of these utility trailers use them), everything is showing power. As I said, I've had the same problem on my 20' utility trailer and on two different rental trailers I had when I rented a bobcat and excavator. I saw on a youtube video that some years had a regulator along the inside of the frame, but I can't find one anywhere on mine. Plus, if the test lights (and my volt meter) are showing power, they should be good.

One other thing- is there suppose to be constant power to the electric brake terminal in the plug? I would have thought that would cause the brakes to be always on. But after checking a post on etrailer.com, it seems this is correct, and that the signal is "searching" for brake connections (??). The two rental trailers I used had surge brakes, not electric, and it's been since last summer that I used my 20 footer.
Thanks for any help or ideas on this. I was about to put in a new plug, but the tester I bought yesterday confirms that it's powering right. 'dunno;
 

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Make sure the grounds on your trailer are good. I had the right side go out because all the ground wires went to a single ground and the terminal on for the right side was corroded. Would carry a voltage but not a load.
 

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Trailer brake power/control is the blue wire which is the signal from your controller. It should not have power unless the controller is sending it because of a braking condition. otherwise you are correct in thinking the brakes would be applied.
Mikey is right-- check all grounds and make sure someone didn't use the ball as a ground point instead of the white wire in the 7-way
 

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Thanks, Mikey. I re-did the brakes last fall after I bought the trailer. It had a surge brake on it and somebody before me (just bought it before I did this) welded up the ram head on the tongue (?) and when I pulled the drums, the pads were worn off, so I installed new Dexter's all the way round and cut off the old hydraulic lines. I'm pretty sure I grounded both sides as well as a main ground at the tongue frame where I spliced in new wiring. Also, the rental trailers had the same problem, so I'm thinking the problem must be from the truck, but I have no idea where that problem is. But thank you for the suggestion. My trailer is down at our property in the sticks right now, so I can't even go out and check that. But when I was using it, I actually went back and checked everything, because the brakes were engaging everytime I used it. I think I even left the plug unhooked to get it down to the property.

I've got a brand new Tekonsha Voyager brake controller. Our 'new' Primus went bad after one year. But what's stumping me is the idea that I'm getting good readings at the truck plug.
 

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My '04.5 Silverado 3500 has been giving me problems for awhile, and I need some help figuring out what's wrong with the system.

On 3 different trailers, I'm getting no right brake or signal light, although the running lights are all working, including the right side. I'm getting power at the truck plug, using a test tool with led's for each function, which shows the right signal light and brake light are sending power to those lights. Except for the "back up" light not coming on (not a problem since none of these utility trailers use them), everything is showing power. As I said, I've had the same problem on my 20' utility trailer and on two different rental trailers I had when I rented a bobcat and excavator. I saw on a youtube video that some years had a regulator along the inside of the frame, but I can't find one anywhere on mine. Plus, if the test lights (and my volt meter) are showing power, they should be good.

One other thing- is there suppose to be constant power to the electric brake terminal in the plug? I would have thought that would cause the brakes to be always on. But after checking a post on etrailer.com, it seems this is correct, and that the signal is "searching" for brake connections (??). The two rental trailers I used had surge brakes, not electric, and it's been since last summer that I used my 20 footer.
Thanks for any help or ideas on this. I was about to put in a new plug, but the tester I bought yesterday confirms that it's powering right. 'dunno;
Since it's multiple trailers with the same issue, it's likely a problem on the truck side.

First thing I'd do is vigorously clean the contacts on the receptacle. The tester you're using probably has little tiny LED bulbs with high resistance; i.e., they draw less amperage than the bulbs in the trailer. The result is that a high-resistance connection at the receptacle (or anywhere in the circuit, for that matter) could make it so that the higher-current bulbs don't work but the low-current ones do. You know this is the case if you pop the bulb out of the trailer and test the voltage at the bulb socket when the light circuit is on; if you read the proper voltage (12-14V) with the multimeter but the bulb won't illuminate when it's inserted, it's because of resistance elsewhere in the circuit.

Failing that, I'd check ground integrity at the receptacle on the truck. In fact, rather than "check" (which is difficult because you need to do it under load, not with just the open-circuit voltage) it, I'd simply add an additional ground tap somewhere and see if that does anything. If you're just doing exploratory diagnostic work while stationary, you could run a wire right back to the negative battery terminal to be sure you have good ground integrity.

I second @sambor's comment on the brake circuit; it should only have voltage when the brakes are applied. On the other hand, the AUX circuit should always be hot.
 

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New thought. In the 2003 time frame GM changed the pin out on the plug where the brake controller plugs in. The pigtails from Kenosha we're wired wrong. Well not wrong, but it took them a while to get new pigtails made. So there are two and it's not necessarily a year thing. GM changed the Yukon's and suburban's first halfway through 2003. And I think the trucks came later.
 

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Most of the truck receptacles have the pin functions on the cover. Maybe yours has the brake wiring connected to the aux pin which IS hot all the time. Pull the plug out so you can get to the back of it and check the colors and make sure no corrosion or broken wires.
Years ago here in Texas we would run into the same brake problems and it would turn out to be what we called "Oklahoma Wiring". They would wire the aux to the brake pin so when we plugged in the brakes would set. Also had one where when we turned the lights on brakes would set. No fun at 60 at dusk.
 

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Only times I’ve ever had issues with the trailer lights it was always a blown fuse in the main fuse box under the hood. You checked those?
 

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Im not sure about the LB7s but my LMM has a fuse panel on the left side of the dash. There are separate fuses for LT Brake/Turn and RT Brake/Turn.

Both are 15 amp fuses.
 

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Before this gets too far into the diagnostics, have you ever pulled a trailer where the lights worked correctly? As others have shared and based on what has been discussed so far I would agree that this is a problem on the truck side. Since your test light adapter seems to be working correctly, I suspect that you have a bad connection to the right brake or signal light lead. The trailer would pull far more current than the test light LED bulbs. Unless you do have some type of oddball wiring these these both would share the same pin on your truck plug. Should be pin #6. Look for an issue there. Maybe rig up a test light using another brake light bulb and see if that will light using test leads.
 

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I think I agree with some of y'all, could well be at the truck plug. My son and I were just arguing about different style of trailer plugs this morning. I still have an old trailer with a 6-round plug that we've been using with an adapter to 7-flat for years. I told him I just need to get it rewired to a 7-flat plug since that's about all we have on all of our trucks now. He was bitching about how hard the 6-round plug is to plug in. I told him yeah, it's hard to plug in but back when that's all we used, we rarely had trouble with a bad connection at the plug. Now we're using 7-flat on everything and fight the plug connection routinely, but they're sure nice to plug in and unplug, nice and easy. I'm always wiggling a plug because of a bad connection causing lack of a light or in the worst case, causing my LML to annoy the hell out of me with the "check trailer brakes" warning continually until I stop, get out and wiggle the connector. The flat connectors don't have nearly as much tension on the connections as the old round pins did.

I'm betting on the trailer plug connection on the truck. I realize it's lighting the LED test light, but as others mentioned, that doesn't take much.
 

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You might try to 'clean' your female side connector terminals by using a gun cleaning bronze brush (I think 22 cal worked for me) and also some Deoxit spray - on both male and female sides. Worked for me.
 

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YEven with a surge brake the truck still has to activate the trailer lights. You can get by with less current with the newer LED lights but for trailers with the old tungsten lamps I would end up running a ground wire from each light up to the connector and not relying on a ground to the frame. The longer the trailer with 12v DC the more likely one will run into problems with the voltage dropping over distance.
 
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