Trailer 7 way connection

[MM60]

I have a 03 tahoe. My 7 way and connecter behind it tests okay for power and brake lights but negative on left and right blinkers. All fuses inside and out are good. I've unplugged the connector and sprayed electrical cleaner to it as well as the 7 way but still no blinkers. Any help with this will be most appreciated

 

[S33k3r]

If the connector behind your 7 way tests negative for blinkers, then there's nothing you can do with the plug -- it's somewhere else in the line.

Some things to try, before getting under the Tahoe and tracing the wires... Get some good fuses -- they are cheap, and you will likely use them eventually. Swap them out. I've found fuses that looked good but still didn't work.

Otherwise, you are going to need to get a wiring diagram and trace the wires from back to front. It sounds like you have an open, somewhere in the line.

 

[iamdub]

It's an '03, so it probably has the updated CAN bus electronics. Maybe the BCM doesn't provide power to these points unless it detects a load? Have you connected a trailer to find the signals not working? With the brake lights just being both "turn signals" on simultaneously, I'd guess that the problem is on the vehicle side. IIRC, there's a connection on or near the frame rail where the factory 7-way connects. After double-checking fuses, test there and work back. Use a test light and not a digital meter.

 

[Fless]

It's an '03, so it probably has the updated CAN bus electronics. Maybe the BCM doesn't provide power to these points unless it detects a load? Have you connected a trailer to find the signals not working? With the brake lights just being both "turn signals" on simultaneously, I'd guess that the problem is on the vehicle side. IIRC, there's a connection on or near the frame rail where the factory 7-way connects. After double-checking fuses, test there and work back. Use a test light and not a digital meter.

The BCM doesn't control the trailer light connection, AFAIK. And as @iamdub noted, there is a wiring block under the right rear quarter panel that connects the various lighting circuits for the back end. Might be good to check there once you confirm the fusebox is providing power.

The underhood fusebox has two separate fuses (L&R) for the TRAILER turn signals / brake lights (and separate from the truck body lights). To be clear, have you verified that those two fuses have power when the turn signals are activated?

I see that you've indicated that the trailer brake light circuit works -- those are the same circuits for the turn signals for the trailer. I would recommend testing the circuits with a regular bulb (more than just a test light) to make sure the circuits can handle the load. Something funny is going on here if the brake lights work but the turn signals don't.

 

[Fless]

I got to thinking about this a bit more, and I BET that the turn signal flasher does the work of combining the turn signal and brake light functions. But do check that junction box behind the RR quarter panel.

On the truck body your turn signals are separate from the brake lights, and are the yellow lens. For the trailer connector, those two functions must be combined so that either one can drive the turn or brake lights on the same circuit. Look to see if your RPO code list in the glovebox lists VR4 as a code, and see the second-last item below from Rock Auto.

 

[MM60]

If the connector behind your 7 way tests negative for blinkers, then there's nothing you can do with the plug -- it's somewhere else in the line.

Some things to try, before getting under the Tahoe and tracing the wires... Get some good fuses -- they are cheap, and you will likely use them eventually. Swap them out. I've found fuses that looked good but still didn't work.

Otherwise, you are going to need to get a wiring diagram and trace the wires from back to front. It sounds like you have an open, somewhere in the line.

Thanks for the info. Using a test light, I get both sides of every fuse to light up when I touch the metal spots on either sides of the fuses located under the hood and inside panel. The weird thing is about 6 months ago one side of the 7 way flashed when the left blinker was on and now I get nothing except for the power and tail lights. I'm wondering if I have a bad ground? I'm going to use your advice and replace the 10 and 15 amp fuses and see if that fixes it.

 

[MM60]

The BCM doesn't control the trailer light connection, AFAIK. And as @iamdub noted, there is a wiring block under the right rear quarter panel that connects the various lighting circuits for the back end. Might be good to check there once you confirm the fusebox is providing power.

The underhood fusebox has two separate fuses (L&R) for the TRAILER turn signals / brake lights (and separate from the truck body lights). To be clear, have you verified that those two fuses have power when the turn signals are activated?

I see that you've indicated that the trailer brake light circuit works -- those are the same circuits for the turn signals for the trailer. I would recommend testing the circuits with a regular bulb (more than just a test light) to make sure the circuits can handle the load. Something funny is going on here if the brake lights work but the turn signals don't.

I did find that panel under the passenger side rear with the 4 harnesses connected to the circuit panel. I took all of them off and sprayed the contacts on both the harnesses and the panel and snapped them back on. Still didn't get blinkers on the trailer. The tail lights on the vehicle work fine. I'm going to replace the panel due to its age. I'm also going to pull apart the wires from the 7 way socket to where they tie into the main harness and check for blinkers and see what happens. I might have a damaged ground somewhere around there.

 

[MM60]

I did find that panel under the passenger side rear with the 4 harnesses connected to the circuit panel. I took all of them off and sprayed the contacts on both the harnesses and the panel and snapped them back on. Still didn't get blinkers on the trailer. The tail lights on the vehicle work fine. I'm going to replace the panel due to its age. I'm also going to pull apart the wires from the 7 way socket to where they tie into the main harness and check for blinkers and see what happens. I might have a damaged ground somewhere around there.

I checked the three 10 amp fuse near the top. Both sides to each fuse light up my test light. When I turn the blinker on the light just stays solid.

 

[MM60]

This is the panel I'm gonna buy

 

[MM60]

I got to thinking about this a bit more, and I BET that the turn signal flasher does the work of combining the turn signal and brake light functions. But do check that junction box behind the RR quarter panel.

On the truck body your turn signals are separate from the brake lights, and are the yellow lens. For the trailer connector, those two functions must be combined so that either one can drive the turn or brake lights on the same circuit. Look to see if your RPO code list in the glovebox lists VR4 as a code, and see the second-last item below from Rock Auto.

View attachment 429111

I will check for that code in the morning. Incidently, that particular 10 pin flasher isn't cheap. $60