Tail lights not working

Hello,

There is a tail light fuse you need to check first to see if there is power there if so follow the power through the switch to see if that is bad here is a guide to help you with the tests.

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

Here is a tail light wiring diagrams and the fuse location to help

Check out the diagrams (Below)

Please let us know what you find.

Cheers, Ken

All of what you described is typical of a broken ground wire, particularly when you have lights flashing with the signals, like the license lamp. To verify this, you can use a test light or voltmeter to check for voltage on all the terminals on one of the malfunctioning bulbs. If you have the flat plastic base with four wires, one should have 12 volts with the brakes applied and a different one will have 12 volts with the tail lights turned on. The other two must have 0.0 volts. With a bad ground wire, you'll have voltage on all four terminals although the two ground terminals will usually not have the full 12 volts.

If the bulbs have the older round brass bases, you must have 0.0 volts on the brass base. You'll find around 6.0 to 8.0 volts there if there's a broken ground wire.

Another clue is when working with the signal lights only, the bulb on one side will act differently when you remove the mating bulb on the other side of the vehicle. That's because when current can't get to ground, it finds an alternate path through the bulb on the other side that it's tied to, then through a front bulb and to ground.

10 gauge is severe overkill. That's good for 30 amps. You need a wire to handle less than 10 amps if it's for all the lights on the rear. 14 gauge is fine for that.

The bigger issue is running a new wire. My students knew that was never an acceptable solution because you don't know what happened to the original wire, so you don't know if the same thing will happen to the other wires in the same harness. As an example, suppose a harness fell down onto hot exhaust parts and one melted through the insulation and the wire grounded out. How long before the same thing happens to the next wire? That second one could result in wasting a real lot of time on the diagnosis when the problem never would have occurred in the first place if the cause of the first problem was found and repaired. You would have seen the other wires in danger of becoming grounded. Same is true when a harness is sliding back and forth on something as the engine rocks, or it's rubbing on a sharp metal bracket. The point is you want to know exactly where the cause of the problem is so you can prevent it from happening again.

Now that you found where on the bulb socket that needs to be grounded but currently isn't, use a test light instead. Ground the test light's ground lead to a good, paint-free and rust-free point. You can even use the end of that wire you used for testing. Place the probe on the point that is supposed to be grounded. When you turn on that light, you'll see the bulb gets only half brightness and the test light gets half brightness. That's because each bulb is getting only half of the 12 volts. Now you can move the test light's probe along the socket's ground wire to the next accessible test point. That's typically a connector. Sneak the probe in there and see if the test light is still half brightness or if it stays off. You're looking for the first place the test light stays off. That means you just passed over the break in the circuit.

Don't get all "wrapped around the axle", (carried away) with searching for every ground wire on the truck. There's only two you have to be concerned with. One is for all the lights on the rear or all the lights on one side on the rear. That wire will usually be in the harness that runs toward the front. It won't be bolted to the box because the box may not provide a good ground, especially if it's mounted on rubber isolators. It could be bolted to the frame. Then you have to look for where the frame is grounded to the body. If that ground is bad, there's going to be a lot of other things that don't work.

The second ground involved is the smaller black battery negative wire. That is bolted to the body, but here again, if that one is bad, everything will be dead because the only other way for circuits to be grounded is through the negative battery cable that's bolted to the engine block. The engine is mounted on rubber mounts. The drive shaft makes a very poor connection, but even if it was good, the rear axle is mounted to leaf springs with rubber bushings. The closest thing there is to another ground path is the accelerator cable, and that will never do a good job.

The most common thing I find when there's a bad ground at the rear is someone installed a trailer wiring harness with Scotch-Lok connectors or something similar. Those don't seal out moisture so you can expect the wires to corrode. Look for rust on the frame too where ground wires are bolted, but that seems to be much less of a problem.

Check the #15 fuse, 20 amp. Also the DRL relay in the convenience center below the dash.

Are you referring to your headlamps or the DRL's? Before you check the relays and such, make sure the bulbs are not burnt out. They are pretty easy to change but if you need help, stop by any auto parts store and they will be glad you giver you a hand.

Check ground at left rear frame rail

Check for a bolt holding several wire ends mounted to frame around spare tire well just behind bumper. Most likely several black wires bolted to one location on the frame. Make sure there is not corrosion or accumulation of dirt on eyelet connector at that point. Remove bolt and clean. Also trace wire up from that point, possible break up farther. If you have a tow hitch, ground is bolted to left side of tow hitch.

It sounds like the turn signal switch is no good but to be sure here is a guide to help you check for power and the wiring diagrams from mitchell1 so you can see how the system works a little better. Check for power in and out of the switch. Check out the diagrams (Below). Please let us know what you find. We are interested to see what it is.