Dome light/courtesy lights

Ok great and what you might want to consider is removing there mess and buying the plug in simple one just like the one I sent a pic of and redo it right then you will have peace of mind that is right. When I say it is plug in simple I mean you unplug the tail light harnes plug this in the middle and put the ground or white wire to good spot on the frame or bumper area and thats it.

Unfortunatly you won't know till you do it. If the problem started right after the instulation of it then you would think it should.

Solving this could get a little messy, but we can start with some easy stuff. Your observation about the radio being on the same circuit is valid, but that is the 12 volt supply for both circuits and it feeds the interior lights all the time. The lights are switched on the ground side of the circuit. That way only one wire has to run to each switch, and the other switches' wires are just tabs that are part of their mounting hardware. The exception is when the switch is mounted to a plastic part such as when GM puts them on the side of the dash pad, or when there's multiple circuits being switch by that switch.

The first thing to do is remove and unplug every door switch. There may be one on the side of the dash and another one on the "B" pillar near the door latch's striker. You'll also have to unplug the head light switch. The rheostat for the dash lights and the dome light switch are two totally different parts of the switch. Also, if there is anything that causes a delay in turning off the lights, you'll have to find that too and unplug it.

At this point, if you measure the voltage on any wire that was connected to a door switch, you SHOULD find 12 volts and the lights should be off. If the lights are still on, you're going to find 0 volts indicating that circuit has a short to ground somewhere. This is where it can get messy by taking a lot of interior panels apart to find the short. Before we get to that point, since the intermittent flickering tells us this isn't a solid grounded connection, consider running around the truck with a rubber hammer. Watch for flickering as you pound in various places.

You are welcome and let me know how it turns out if we need to go deeper then I will see what I can do ok. Thanks for your support too.

Next, remove the dome light assemblies. Some designs have socket terminals that can touch the body if they aren't positioned correctly, particularly those that use the tube light bulbs that have a round cap on each end. These assemblies often get their ground circuit through the mounting screws.

This is where it gets messy. An orange wire feeds the 12 volts to most of the lights. They have white wires that get grounded by any of the switches to turn all of them on. Those white wires run to every light socket and to every switch. If any of those wires has rubbed through the insulation and is touching the body, all the lights on that circuit will turn on. If you can't find a clue as to the location of the short by wiggling and tugging on the wires, you have to start cutting them apart. Later you'll have to splice all those cuts back together.

Think of having a leak in an underground lawn sprinkler system. There's no way to tell where the leak is. All you know is water is flowing through the main pipe. To isolate the branch with the leak you would have to block each circuit until the leak stopped. That means turning off various valves to the individual branches. Cutting a wire is like closing a valve. The only problem is soldering and sealing all those cuts takes a lot more time then turning a valve.

Yup. The white wires go to ground through the switches, not directly.

If the overhead lights come on and the floor ones don't, there has to be an open in the wiring. Basically, a wire is disconnected or broken. Trace the wiring back from the lights themselves to see if you can find a problem. Also, use a test light to see if there is presently power to the light socket. You may even have a ground issue, so make sure the test like has a good ground.

There should be a small push in door switch close to the hinges, so when you open up the door the switch comes out. Make sure the switch isn't stuck inward.

That will work, here is the wring diagram for you so you can get the problem fixed.

https://www.2carpros.com/articles/how-to-use-a-test-light-circuit-tester

Please run this test and get back to us so we can continue helping you.

Best, Ken