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taillight short

Discussion in 'Chevy Trucks' started by Detroitdan, Dec 24, 2007.

  1. Detroitdan

    Detroitdan PlowSite.com Addict
    Messages: 1,937

    I have some sort of an intermittent short in my taillights. Other night the wife noticed my taillights were on at 2am. Went out and checked, odd thing is it was only the two taillights, not the front parking, marker or clearance lights. Wiggled and jiggled lots of wiring, couldn't figure it out. Unhooked the batteries and went back to bed.

    Decided it was a bad headlight switch, it's acted up in the past, quite often I have to fiddle with it to get the lights to work. Bought a new one, no difference. Even with the switch unplugged they still light up. Also, they will dim and brighten every now and then. Pulled fuses relating to lights, no change. Don't know where it's getting power from. Truck has a lot of factory marker lights because it's a dually, why aren't those lighting up too?

    Lastly, I noticed the dome, map and rear cargo light don't work. Must be related.

    Recently I had the dash apart to change the shifter. I also have a remote starter, so in addition to my plow wiring, sander, gauges etc, there is a lot of extra wire under the dash. So I'm leaning toward it being under the dash rather than a trailer wiring problem, although I have backed into some snowbanks recently. After fiddling around I got the problem to cease, now I notice my lights no longer flash when I remote start it or unlock doors. Another reason to suspect the remote starter.

    There must be some powered wire under the dash that is coming into contact with something in the tangle of wires. Still don't understand why it's just the two taillights. It is definitely not the brake lights, they work when I step on them. Unless...if the brake lights are only getting a little voltage, not enough to look like brake lights. That would explain why the markers don't light. Now I'm thinking more along the lines of the brake light switch under the dash.
    Or maybe something in the third brakelight, which is where the cargo light is that stopped working...
  2. wild bill

    wild bill PlowSite.com Addict
    Messages: 1,239


    you might check the taillights them self's in that year range they have a circuit board for the bulb's them self's take them out they are prone to corrosion .they can be had after market i know from o'reilys auto parts .just a idea .
  3. Detroitdan

    Detroitdan PlowSite.com Addict
    Messages: 1,937

    That's a good idea. I have seen people need to replace them before. And mine must be getting corroded to heck with the mix that's been on there right up against the tailgate for weeks. If I ever get a chance to get the tailgate sander off and clean the truck out, I'll pull them out and take a look. Actually, I can pivot the sander out of the way to get the tailgate open.

    Still gotta wonder about the dome light and third brake light not working. I wonder if something got into that and shorted it was causing the lights to come on, then a fuse might have blown which is why those lights are out now. But I still have brake lights...

    Odd thing happened last night, I started it with the remote, and like I said the parking lights didn't come on like normal. I checked the brake lights to make sure they were working, and they were. Then I realized that stepping on the brake is supposed to shut the truck off when it is running from the remote, but it didn't. So some of the remote start functions are no longer working, but it does start the truck.
  4. nicksplowing

    nicksplowing PlowSite.com Addict
    Messages: 1,226

    If You Had All The Fuses Out Relating To The Lights You Can Elminate The Circuit Boards.........sounds To Me Like You Have A Short To Power Somewhere Else Steering Column Or Underdash Etc. .......have You Drilled Any Holes Recently Thru Firewall I Cant Tell How Many Times Ive Seen That Happen In Plow Trucks specially Good Luck Keep Us Posted
  5. Detroitdan

    Detroitdan PlowSite.com Addict
    Messages: 1,937

    had the dash off last week to replace the shifter I broke. Guess the dash is coming off again.
  6. Detroitdan

    Detroitdan PlowSite.com Addict
    Messages: 1,937

    Went out this afternoon and they were on again. Had no time to check anything, just unhooked the batteries and went to work. Now tomorrow I'll hook them back up and it probably won't do it for me.
  7. wild bill

    wild bill PlowSite.com Addict
    Messages: 1,239


    i take it is a after market remote start ,man they can be a never ending series of problems .causing mystery problems
  8. Detroitdan

    Detroitdan PlowSite.com Addict
    Messages: 1,937

    You're probably right. Maybe I'll try shutting the starter off by it's switch, see if that makes a difference. Almost tried that the other day when they were on, but I got sidetracked. Installer said it is possible the wiring could backfeed and I might be able to fix it by installing a diode to make the wires one-way. But he said I really shouldn't have to. Starter has been in for a year with no problems before now, but I did have the dash apart and probably roughed up some of the extra wiring. Starting to feel a little better about maybe figuring this out.
    Thanks for the support.
  9. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    Shorts and back feed problems can be a real time consuming things to figure as most know but the first thing I'd do is disconnect the remote start from the truck and see if it fixes the problem.

    The tail light circuit boards can't cause it to do what yours is doing.. because theirs no power of any kind at the tail lights unless the lights themselves are turned on.

    In fact, there should be nothing powered with the key and lights off on the truck from the rear of the cab to the rear of the truck (including the cargo and 3rd brake light). The only thing that will have 12V with the truck off in the rear is if your trailer plug has a charge wire...it's usually hot all the time, but nothing else will be. So I definitely be looking around under the dash for problem.

    If you can determine if it is in fact the brake or the tails that are staying on, would make it much easier to pin point the trouble though.
  10. sparky8370

    sparky8370 Senior Member
    Messages: 234

    It could if something connected into the load (the remote starter in this case) is hunting for a ground (ie:it has a bad ground). It would create a series parallel circuit and the lights would be dimmer than normal.

    Just hypothetically speaking, say the remote starter is a 10 ohmn load, and the lights are a 5 ohm load. In this example, it's just a series circuit as we are counting the whole remote as a load. In series circuits the resistance is additive, so there is a total load of 15 ohmns. So 12 volts/15 ohmns= 0.8 amps. The amperage is the same across the whole series circuit, but the voltage varies at each load. The starter will have 8 volts and the lights would have 4 volts. Now if they were both the same resistance than they would get equal voltage regardless of the amperage.

    formulas used here: Volts/resistance=current
    current x resistance=voltage
  11. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    Yes, but the fact that they're "dim" isn't the issue, it's the fact that there on at all.

    I think you missed my point sparky, the tail light circuit boards failing is common problem on the 88-98 trucks... and a corroded or failing board won't directly cause the lights to be on when they shouldn't.

    And like I said, it sound's like a back feed problem... which would be the same as "hunting for ground".... but again the circuit boards themselves wont cause it.
  12. Detroitdan

    Detroitdan PlowSite.com Addict
    Messages: 1,937

    First thing I will check is the ground for the remote starter, if Ican find it. I remember disconnecting a ground wire for something when I pulled the dash, I put it back but maybe not well enough.

    Another thought, I lost the light in my 4x4 indicator recently, didn't think much of it, figured the little 194 bulb finally blew. But with no interior lights maybe that had something to do with it too. But I do have dash lights. And the 4x4 shifter does light up, just not the actual indicator.

    Going to check fuses again, must be something blown to have no dome or map lights.

    Thanks for all the help, electrical has always been a challenge for me. Along with almost everything else.
  13. Detroitdan

    Detroitdan PlowSite.com Addict
    Messages: 1,937

    I don't know if my trailer wiring has a charge wire, but I think it does. Don't know when it's powered up or not. I actually have two plugs, one 7 pin RV for my camper, and one 6 round for my landscape trailer. I have a 4 pin flat adapter hooked into my 6 pin, into which I've plugged my sander mounted light. So the light runs with the parking lights if I plug it in. But I checked that. Didn't look at the 7 pin cause theres nothing in it, but perhaps it got wet, corroded or otherwise damaged. One more thing to check. I certainly stuffed the rearend into a lot of snowbanks in the last couple weeks. My sander has been on the whole time, which is unusual. Normally I take it off, but my garage is a mess and I haven't had room for it and I've just been lazy and busy and whatever.
  14. REAPER

    REAPER 2000 Club Member
    from 60050
    Messages: 2,230

    Seems you are concentrating to much on the remote starter when in fact you said it was working fine for a year.

    I would check your trailer plug connection for corrosion.
  15. Detroitdan

    Detroitdan PlowSite.com Addict
    Messages: 1,937

    Ladies and gentlemen, we have a winner!

    Very first thing I checked was that trailer plug, but I just reached down and tugged on it and twisted a bit, didn't really check it properly. No flicker from the lights, so I convinced myself to look at the dash mess, since I just had the dash off the other day. Pulled the dash again last night, found a melted fuseholder for the starter, but nothing I did would make the lights go off. So I finally made my way back to the back of the truck, by this time the lights had been stuck on for over a half hour. Soon as I touched the 6 pin trailer plug I could feel it was smoking hot. When I installed it years ago I was careful to wire it nicely and seal it up tight with silicone, but it looks like the salt finally got in there. And I suspect running my sander light off of it , even just for short periods of time, was probably too much draw and helped it on it's way out.
    What a relief to have finally figured this one out. Thanks for all the help and input.