I was pulled over the other night by an officer, and they told me my rear tail lights were not working right. They were very dim except for when I hit my brakes. Luckily, he had me turn on my flashers and drive with them until I got home.

What could be causing my lights not to work properly? When I turn on the headlights, my tail lights are on, but they are very dim. I have checked all of the fuses, but they all look fine. Also, my front marker lights seem to be working along with my rear brake lights.

One other thing is that when I lock my doors with my keys, some lights used to flash on the front and rear, but now nothing flashes. I am not sure which lights are supposed to flash though. I have also checked the rear bulbs, and they look fine. Any help is greatly appreciated. Thinking it might be a short somewhere but am not sure if that sounds right.

 

Might be a ground wire somewhere, or a short.

 

Yep, check the grounds, also pull the bulbs out of the socket and clean the contacts on the bulb and the contacts inside the socket. They can get corroded and cause issues. Put some bulb grease on them as well. I would suspect the bulb contacts first though.

 

bad ground maybe. the directionals all flash when you hit the key fob. Basically the computer activates the hazard lights when you press that button with the addition of cargo and interior lights after you hit it twice

 

Would there be a ground wire associated with the light symptoms that might would cause this? Just trying to find a place to start looking. I don't have much electrical experience, so this will be new to me. Any help on the best way to trace down a bad ground would be greatly appreciated.

I do not think that it would be the bulb socket since both sides are acting up, or is that not an assumption that could be made?

 

One wire ran to the back of the truck for the running lights then it splits.
That is helpful because you need to trace the wires before the first taillight. You will see the wire loom and can trace it back to the front. You might have hit something or ran over something and it smashed it somewhere, and you may have more wires to replace than one.
That's for the power wire, but the ground wire would be screwed to the truck somewhere. I don't recall where exactly, but mine is pretty modified when it comes to the wiring due to having a brake controller and 7 pin hookup back there, as well as a 4 flat that plugs into the light wiring. When you find what you think is the ground, you can take it off, clean everything up, and maybe even find another better spot to put it as it's probably rusty right there anyways.

 

If you can't find the ground wire attachment point from the harness, find the ground wire from the first tail light the harness comes to (this is usually a black wire), next, get a length of #16 or 18 black wire long enough to go from the engine bay to that light, following the way the harness goes (this is so you can tape of use zip ties to hold that wire to the harness so it doesn't flop around). Now splice that wire into the black tail light ground wire and attach the other end to any small nut or bolt around the engine bay (you're just trying to make a good ground contact here, so don't get too exotic) - I'd look for a place on the firewall. Some people would make a hole in the firewall and then use a self tapping screw, but some of these people have also been know to drill a hole into something important on the other side of the firewall, so I'd stay away from that and just look for a firewall ground connection - you can usually find several braided cables connected to the firewall for engine and body ground interconnections & I'd use one of those. This should give you the ground you need and then check the harness connectors to the lights as well as the bulb sockets for corrosion. Use a di-electric grease on them to slow down corrosion.

 

I would start with the easy things first. Check the bulbs anyway.

 

As jkeaton mentioned, do the simple stuff first, also, many of your checks will require you to take off the tail light covers. Once you do that, here's a quick list of what I'd do:

• Check bulbs and sockets for corrosion,
• Using a multi-meter, check the voltage at each lamp socket. If you get 12 volts, I'd try a new bulb & if you don't (with both dim, you'll likely see something substantially lower than 12 volts. This would be a result of a poor ground or poor connection someplace - something that would give you a high resistance.
• If I had the low voltage, the next step would be to determine if the resistance was in the ground or +12 supplied to those lamps, and I'd start with the ground. The flashers etc. use a different circuit, and if they work correctly, their ground would be good, so I'd do the following :
  • Turn your tail lights on, then
  • Using the multi-meter, put the plus (+) probe onto the center contact in the faulty bulb socket,
  • Put the negative probe onto the casing of the flasher bulb socket,
  • If the ground is poor on the tail light circuit, you should now read proper voltage because you're using a different ground source for this test.
  • If you still get a bad result, do it the other way, probe the +12 from the flasher circuit and the ground from the tail-lights (with the flashers on for this test, you'll end up with a "pulsing" +12 showing & if the flashers are off, you'll get nothing )
• If it's the +12 supply that's got the problem, you can also do a long wire solution, but where to take the source gets a little more complicated, so I'll save that diatribe for later - the problem is usually a bad ground for multiple dim bulbs.

 

If you must splice into a wire be sure to do it right or it will come back to haunt you in the future. Solder and heat shrink tube (the good stuff with the sealeant) is the only reliable way to splice.
If you pull the taillights its a good time to spray some rust preventative into the seam over the rear wheelwells.