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Discussion Starter · #1 ·
Last night the wife tells me she looked outside and saw my taillights were on. So I go out to investigate and couldn't figure it out. Ending up needing to disconnect both batteries just so I could go back to bed. Still couldnt get back to sleep because of trying to figure it out;)
Here's what is strange: only the two taillights were on. Not the plate light, or the front parking lights, or any of the numerous clearance and marker lights my dually has. I checked the trailer light plug, tried looking in the tailgate but I can't open it because I have my tailgate sander on and 1000 lbs of sand on right now. The only power at the rear of the truck is the heavy gauge 12v for the sander, but that is off with the key I think, and even so if it doesn't appear to be damnaged. If it were I think it would burn the truck down.
I can't figure out where the two lights are getting power from. Seems if it were bleeding in at the switch wouldn't it light all the lights? I thought the power going out of the headlight switch ran every parking circuit light. If not, then there is my problem, because my headlight switch is a little sloppy from age. Also, while I was looking at it, the taillights went out and came back on slowly a couple times. Like a weak connection, maybe something to do with corrosion getting in sopmewhere? There was a lot of snow, maybe some was starting to melt and get in somehwere? The truck had sat for a couple days before this happened, so it was cold.
 

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sure it's not brake lights? might want to check your brake light switch under the dash???
 

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X 2.
 

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if i do recall i hade a minor issue with fuses and found in the fuse box by the battery there is a relay for each side, tail light and blinker, so there might be a possibilty it is the relays. Good Luck
 

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Discussion Starter · #5 ·
thanks for the input, all good ideas. I thought about the relays for both sides, I know they do that on newer trucks but I don't think mine has it. And it is not the brake lights, I thought it was at first even though the third brakelight wasn't on, cause they seemed pretty bright, but it was just cause it was so dark out and they were shining off the snow. When I stepped on the brake the brake lights came on.
Upon further investigation I now can't get the parking lights and marker lights to come on at all. In fact the switch seems to hang up a little when you try to shut it off. In the past this has happened and I've had to jiggle the switch, so I suspected the switch was going bad. In thinking about it I realized that a zillion of these trucks came without all the rear markers my dually has, so they must come wired up seperately. Bought a new headlight switch today, will install it tomorrow, see if that fixes it.
 

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All good things to check, i would go after the trailer plug/harness also for corrosion. Especially since you said you have a sander.
 

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Discussion Starter · #7 ·
well, I just replaced the headlight switch, no difference. Even with the switch unplugged it still does it. I messed around under the dash and they are out now, but I don't know if they'll come back on. I tried pulling all the lighting fuses, that wouldn't shut them off, so not sure where they are getting their power from. Now I'm stumped. I have an unbelievable tangle of wires under the dash, the remote starter ties into the lights, my plow harness ties in, there's just too much multi-colored spaghetti under there. I suspect I may have messed it up the other day when I pulled the dash off to replace the shifter. And it's probably just some random wire shorting against something else, might go away for a while or might stay and cause real problems. When it was on I noticed it tended to go off and on real slowly occasionally. No idea what that means.

Gonna have to get under it and look over the taillight and trialer harness, I've been plowing and sanding and backing into a lot of snowbanks.

Don't know if it's related, but I think it may be- I just noticed the dome light and map lights don't work, or the cargo light. Now where could they be connected? Somewhere in the harness off the switch?
 

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Discussion Starter · #8 ·
All good things to check, i would go after the trailer plug/harness also for corrosion. Especially since you said you have a sander.
Ding ding ding! We have a winner! First thing I checked, but I didn't really check it, just gave it a twist and tug, didn't get a flicker from the lights so I talked myself into believing it had to be related to the fact that I just had the dash apart. So after pulling the dash apart again, and finding nothing of interest other than a burned, melted shorted out fuseholder for the remote starter, that melted so bad it had power flowing through it after fuse blew. I went out back to take a closer look at the trailer plugs. Now the lights had been stuck on for a while this time, so as soon as I touched it I felt the heat inside. It was the 6 pin female trailer plug. When I installed it years ago I was real careful to seal it up with silicone to keep it dry, but years of backing into snowbanks and sanding apparently allowed crap in there and it just shorted and melted itself inside. So the trailer power was powering up the park lamps. It got so hot I can't believe I didn't have a fire.
What a relief to have slain that gremlin. Thanks for the input guys.
 
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