Wiring Gremlin

[USMC1188]

I have LED Anzo taillights on my truck. I noticed a while ago that my driver's side taillight would not work when I had my headlights on. It would still work with my turn signal and brakes, just not the running lights.

To maybe get it working again, I just rednecked it and wiggled all of the wires around going up into the taillight assembly and it worked again fine for a while. So that means there is a short of some sort in the wiring for that taillight as everything else works fine.

My mother in law was behind me last night and noticed it was off again. So I just decided to give it an easy wiggle again and just get it going again for a while... well, it didn't work this time.

Now, I still have no taillight, my brakelights still work fine, and my turn signal isn't working (sometimes). So I took the assembly out this afternoon to maybe narrow down the short and get the problem resolved for good. We took a multimeter to the wires and see what we could get.

We got 2 volts constant on the taillights (should be around 12 correct?)

We got nothing on the brakelights (even though they still work fine... which makes no sense to me)

There was nothing on the turn signals either.

So to confirm my dreaded suspicions, I took the driver's side taillight assembly and plugged it into the passenger side.... everything works fine.

That means, its not the wiring in my taillights, but the wiring in the truck itself.

My question becomes, what is my next step. Is there a somewhat easy(ish) way to narrow down which section the short is in? Is there a wiring diagram for the lights? Does anyone have any advice on how to proceed?

 

[MegaMouseGW]

Ah the dreaded wire eating gremlin. Easiest but not the cheapest solution is to replace the entire bed wiring harness. Should be able to get it through the dealership or Truck Parts & Truck Accessories for Chevy, GMC, Ford & Dodge Trucks | LMCTruck.com . Or bite the bullet and have the dealership check your TIPM for failure.
When you checked the lights did you have someone stomping on the brake pedal when you checked the brakes for voltage?? Also the turn signal will go on and off and you will need a fast voltmeter to read the spikes. There should be NO voltage present at all when the lights, the turn signal, and the brake pedal are not on. Sounds to me like bad wiring.

 

[USMC1188]

Ah the dreaded wire eating gremlin. Easiest but not the cheapest solution is to replace the entire bed wiring harness. Should be able to get it through the dealership or Truck Parts & Truck Accessories for Chevy, GMC, Ford & Dodge Trucks | LMCTruck.com . Or bite the bullet and have the dealership check your TIPM for failure.
When you checked the lights did you have someone stomping on the brake pedal when you checked the brakes for voltage?? Also the turn signal will go on and off and you will need a fast voltmeter to read the spikes. There should be NO voltage present at all when the lights, the turn signal, and the brake pedal are not on. Sounds to me like bad wiring.

I've already started looking into an entire new wiring harness, but I am going to start by sectioning it out and checking for power throughout the wiring harness and hopefully narrow it down.

I had someone helping me with it all, so if it any of it was good, we would have gotten the correct signals.

 

[MegaMouseGW]

I've already started looking into an entire new wiring harness, but I am going to start by sectioning it out and checking for power throughout the wiring harness and hopefully narrow it down.

I had someone helping me with it all, so if it any of it was good, we would have gotten the correct signals.

Help is always accepted. Glad you had some in attempting the troubleshooting. Realize that the bed harness is several pieces. It might be just one piece or a couple.

 

[USMC1188]

Help is always accepted. Glad you had some in attempting the troubleshooting. Realize that the bed harness is several pieces. It might be just one piece or a couple.

From the research I have done, it is in at least a couple pieces. My next step is going to be to find all of the connections as it heads towards the front of the truck and test every one and hopefully narrow it down.

 

[USMC1188]

Alright, its getting worse.

I have not had a chance to do any more investigation into the issue, BUT, I have been getting the lamp out ding off and on at random times, as well as the bulb out fast left turn signal sometimes as well (which would say short right?). The strange part is when I get the fast turn signal, the rear led turn signal as well as the front still work.

This morning, I am got the lamp out ding EVERTIME I hit the brakes.
It also did the fast flash everytime I turned on my left turn signal. When I hit the turn signal, it starts normal, then dings, and goes fast, it doesn't just start out fast right away. Again, both the brakes and turn signal still work, but the taillight itself doesn't.

Ideas?

 

[USMC1188]

Alright, I think I finally got this problem solved for good. I want to post the fix here just in case anyone else ever comes across the problem.

We ended up finding 2 shorts in the wiring going to the left taillight. Neither wire was broken all the way though, just the copper wire inside, so it was next to impossible to find. Once we fixed that, the taillight worked find, but we still got the fast flash on the turn signal, and ding with turn signal and brakes. I narrowed that down to the resistor in the led taillight itself. So today I cut out the old resistor and put in a new one... so far so good!

Here is the old crappy resistor cut out:


And the new resistor in its place (the yellow box):


I bought the resistor from superbrightleds.com for only a few bucks... so all in all, the entire fix was less than $20... but it was a HUGE headache.

 

[MegaMouseGW]

Glad you got it fixed. Wiring gremlins can be the hardest things to tackle for anyone.

 

[USMC1188]

Thanks! You aren't kidding!

 

[Redtruck-VA]

Well done...

 

[Harley Harrold]

I know that when I worked as an auto mechanic, they would always give me the electrical problems to fix. Sometimes the fix was quick, other times it would be an all day sucker. I am glad this was in the early years before computerized components were incorporated into the mix.