Mysterious mystifying running lights problem

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Mysterious mystifying running lights problem

Postby bluebanjo » Thu May 25, 2006 11:12 pm

Okay kids, I am stumped on this one. I just rewired my TTT (aka my 1965 Shasta Compact, "Sparky the Wonder Trailer.") My wiring harness on my tow vehicle isn't working right now and I am trying to test the trailer lights by using a lawnmower battery. I will get the tow vehicle fixed next week.

So I hook up my trusty lawnmower battery and everything works. There are only right turn, left turn, brake lights, a license plate light, and two side running lights per side -- an amber and a red per side. Only outside lights -- no 12-volt inside lights at all.

Everything works I say -- except the amber and red side running lights. Wierd. The bulbs are new -- in fact I replaced the old running lights with brand new ones. The license plate light runs off the running light circuit (brown wire) on the door side and my 12-volt tester shows the wires are hot, the light sockets are hot -- but somehow the side lights don't light up. The back running lights, however, work like a champ and just like the license plate light, these lights run from the same circuit.

Doh! I can't figure out how the side lights can't work when other lights that run from them work okay.

Any ideas out there? I think I might possibly be losing my mind. But that's okay, I can probably pick up another one at HD.

:thinking: :thinking: :thinking: :fb
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Postby rainjer » Thu May 25, 2006 11:21 pm

Only outside lights -- no 12-volt inside lights at all.


Normally the inside lights do not run off that circuit. They should have a separate battery.


Doh! I can't figure out how the side lights can't work when other lights that run from them work okay.


Sounds like a bad ground on those light. They normally use the mounting screws as the ground.

Are the lights attached to metal or wood?
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Postby madjack » Thu May 25, 2006 11:29 pm

...yep, pretty much what Rain just said...when you rewired, didja ground the body...the side markers probably ground to the body.......
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Postby Nitetimes » Thu May 25, 2006 11:58 pm

madjack wrote:...yep, pretty much what Rain just said...when you rewired, didja ground the body...the side markers probably ground to the body.......
madjack 8)


Yup, what he said^^^. If the lights only had one wire make sure whatever you mounted them to is grounded well.
If all else fails you may need to run ground wires to each light.
A simple test...hook up your hot wire...remove the light lens and touch a wire from the battery ground to one of the mounting screws. You should be able to tell which one by the metal strip under it.
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Postby bluebanjo » Fri May 26, 2006 10:22 am

Thanks guys! I will check to see that everything is properly grounded. If I can fix the problem I'll report back.
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Postby bluebanjo » Fri May 26, 2006 6:46 pm

Yep that fixed it. I rechecked all my grounds and now everything works correctly. Thanks a million guys! You just saved me even more time and money than the last time this forum saved me a bunch of time and money. Now -- on to the insulation, the panelling, the floor, and every other little thing I have to figure out. :applause: :applause: :applause: :D :D
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Postby cracker39 » Sat May 27, 2006 7:30 am

Weak grounds can also cause problems. I had a really weird one with my boat trailer. When I'd step on the brake, the turn signals would stop blinking and both would come on, and they are separate lights and a different circuit, as my truck has separate turn signals and I wired my trailer the same way using a 6-wire connector set. I also have a ground wire and do not depend on a frame ground (same with my TTT).

It was a mysterious problem. I could connect a hot wire to each wire on the trailer and each light worked correctly. I tested the connector on the truck and the same...I had 12 volts coming from each "prong". I even rewired my ground wiring and that didn't help. Finally, I took the plug out of the socket on the truck, and spread the ground "prong" in the socket wider (it has a split in the end) so it would make better contact with the "hole" in the plug and that solved the problem. It was getting a weak ground. I don't know how that made the lights go crazy, but it did.
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Postby bluebanjo » Sun May 28, 2006 2:20 am

Now that I've packed every little inch of the trailer with brand-new styrofoam insulation, I'm waiting for the rain to stop (Seattle, what else) so I can get in there with my 12-volt lawnmower battery and check things out again before I seal the whole thing up with new ply. Man, grounding lights is a wierd science. Thanks for your experience. It's good to know I'm not the only one out there scratching my head.
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