I have a 07 Silverado new body style that's parking lights and the brake light on the passenger side do not turn off I have to disconnect the battery every time I'm out of it for more than 3 hours or so I can take out the fuse for the driver side but the passenger side stays on even without the fuse I have gone through everything short of tracing every individual wire to find the problem I checked the fuse box the trailer plug and have been all over the web to try to fix this problem

 

strange that it's only one side. There must be a short in the right side wiring. I'd start by looking in the lamp assembly. Then check the junction block



Then the underhood fuse block, and finally the harness.

 

Did all of that but thank you

 

Here’s a few checks to make - diagnosis can take a lot of different paths depending on the results of each of these tests, so instead of explaining every possibility, report back if any of the lights go out and which ones.

I recommend hooking up a jump pack or battery charger to provide additional power and keep the battery from draining during the testing.

Also these don’t have to be done in any specific order - I’m just trying to list them starting with the easiest.

1) Turn the headlight switch to the off position instead of leaving it in the auto position.

2) Pull the park lamp relay (underhood fuse block).

3) Fuses - you said you tried pulling fuses already, but did you know there’s fuses both under the hood and in the cabin for the lights? Pull EVERY fuse (not just the park lamps) that has to do with the lights - note which lights turn off with each one.

4) There is a junction block for the rear lights on the frame rail near the spare tire (see illustration below). They are known for having corrosion problems - it’s possible a short in this junction block is causing feed back to the front. Remove all the connectors and inspect for corrosion - it’s much easier to do if you have an air compressor for cleaning the crud out. Dirt gets packed into the release tabs and makes it difficult to remove them. You don’t have to drop the spare to see it but it will give you some more working room.



#2 is junction block

 

Ok I went through the list of stuff you recommended nothing changed when I pulled all of the fuses in the cab and under the hood just the driver side turned off and i checked the junction box in the back and aside from the dirt on the outside of plugs there was no signs of corrosion and the same goes for the fuse block in /out all 3 look to be in good condition

 

If nothing I suggested made a difference, the location of the problem can be narrowed down by working from the rear junction block and lights, even if the short turns out to be ahead of the junction block. I understand the harnesses may look good externally, but that doesn’t mean there’s no damaged wiring inside them.

In case you’re curious, I suspect the problem lies with the rear wiring for the simple fact that the right brake light is on. If the problem was ahead of that (shorted headlight switch, for example) I’d expect it to affect both brake light circuits because there’s a common feed from the front to the rear lights. That doesn’t mean it can’t be ahead of the junction block, but the following steps should determine if that’s the case.

Here’s the sequence I would work in. Assuming no changes, proceed to the next step, making sure to undo that step (for example, if removing a bulb, plug it back in). If one step turns off the lights, the problem is isolated to that circuit.

1) Remove the right upper brake light bulb.
2) Remove the right lower brake light bulb.
3) Remove the right marker lamp.
4) Remove the right license plate lamp.
5) Unplug the right side brake/turn harness at the junction block (bottom middle connector, has a black face).
6) Unplug the right/left parking light harness at the junction block (far right connector, has a purple face).
7) Unplug the left side brake/turn harness at the junction block (top middle connector, has a gray face).
8) Unplug the primary harness at the junction block (far left connector, has a blue face).

I would expect unplugging the primary harness at the junction block will shut off the lights, but if the front lights are still on, the short is in the primary harness along the frame rail.

If you have a trailer plug, is it factory or aftermarket? If aftermarket, is it spliced into the wiring or is it a plug and play setup? If plug and play, you can add removing the trailer harness into the steps when it seems convenient. I know later model GM’s included an extension harness for factory trailer plugs to add a bed plug and I’ve seen some of those cause trouble, I just can’t recall if they were on the 2007’s.

 

Just ran through all the steps if unplug the box the lights in the front stay on and when you say primary harness are you talking about the fuse box or is there another harness somewhere and the trailer plug is stock

 

By primary harness, I mean the harness that runs along the frame rail from the engine bay to the rear junction block - it has all the power feeds for the rear lights.

If the front parking lights are still on after unplugging the primary harness at the junction block, the problem is within the harness itself, isolated to one of the fuse blocks, or one of the controls (headlight switch or BCM). Before you start ripping apart the harness, see if pulling one of the front parking lights causes them to turn off.

I’ll have to look at the wiring diagram again to determine the next steps.

 

How do I tell if I have a bad bcm

 

The general rule for modules is “test the inputs and the outputs.” You need to verify all the power (direct battery and ignition fed) and ground feeds are good. If those check out ok, you need to check the output control circuits - in this case, you want to back probe the parking light control circuit at the BCM and monitor whether or not it’s turning off when it should.

I can’t recall the exact time, but when the ignition is shut off and the door opened, the BCM initiates an exterior bulb check for 10-30 seconds (might be user adjustable from truck to truck). If you know they’re supposed to shut off after 10 seconds, you’d be watching a meter to be reading battery voltage during the bulb check and then no volts when the bulb check is complete.

Regarding your situation in particular, if there’s a short to voltage in the harness (as opposed to a faulty BCM), the meter may still read battery voltage at the BCM even if the bulb check is completed because that short would be powering the park lamp circuit. At that point, you’d want to unplug the BCM to check for a short to voltage.

I understand this is a frustrating situation, but the diagnosis needs to methodical. At this point you’ve ruled out anything from the rear junction block on back as the source. Although I did forget to ask you - is the trailer wiring spliced into the primary harness? In other words, is it spliced “before” or “after” the junction block? If before, when you were pulling fuses, did you also pull fuses for the trailer plug (lights and the 12v feed)? Just want to be thorough and make sure the trailer plug/wiring is ruled out - it’s amazing the problems they can cause sometimes.

Do you know how to read wiring diagrams? I can get them posted tonight.