[HO455]

Usually when you have problems like yours it comes from poor grounds. Electricity takes the path of least resistance and that path can at times be though other lights.


Your Suburban taillight housings need to have good electrical connection to the body.

To troubleshoot this I find it easiest to use a 20 foot long test lead. Hook one end to the negative post in the battery and use the other one to ground the light housing when the turn signal is operating. If the housings ground is poor it should start operating correctly when you touch the test lead.
You may find that you have to touch the metal part of the bulb socket to get the light to work correctly. If so there is corrosion under the crimped area of the socket where it attaches to the housing.

Once you determine the ground is bad you need to remove the housing and clean the mounting bolts and the area around the holes they go through there needs to be shiny metal to metal contact between the body and the housings. I use copper anti-sieze to coat the shiny unpainted areas, it allows good electrical grounding and keeps those areas from rusting.

GM used star washers to cut into the paint and get the housings to ground. However GM used no compound to prevent rust so eventually the housings loose there electrical connection. It was fine for the assembly line and getting through the warranty period.

On your connections the second connector on the drivers side should be te fuel tank sender wire. And if memory serves me correctly the back up lights..

On a Suburban the rear harness runs up the driver's side A pillar and back above the windows to the driver's side rear corner where there is the passenger side wires split off and cross over the rear doors/hatch. Both sides drop down to the areas in your pictures.
The wiring colors will match the pickup colors in the harness schematics post here on the forum.

There is a connector under the dash in the area of the headlight switch where the rear harness connector plugs into the Suburban ONLY under dash harness. I say Suburban only but I don't know for sure if Panels use the same set up. I do know that a pickup harness won't work without a bunch of work.

I don't know of a Suburban specific trailer harness but a call to M&H or AAW would confirm that. A low volume harness like that isn't likely to be listed on their websites.

Good luck and keep us posted on your results,.