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Old 09-17-2017, 11:03 PM
sailorbyday sailorbyday is offline
TT Newbie
Join Date: Sep 2017
Boat: 71 mariner
Location: midwest
Posts: 1
Running Lights Won't Work

Have the chronic issue where brake and turn signal lights work but running lights don't. I believe I have some strange grounding issue. Here's what I've done:
1) With a multimeter, I verified that I'm seeing 12V off of the round to flat adapter plug for my 2004 Silverado.
2) With the wire harness attached to to the flatplug on the truck, I've cut (and since recrimped) the running lights wire and verified 12 volts of the trailer harness.
3) I have a 'Y" for the running lights wire that lead back to each light. I only have one light (back right) wired to the 12V brown running light wire (no side markers are hooked up). I verified I have 12 V off each end of the brown Y ends.

I have the ground wire running all the way back to the back right light mounting bracked and have the ground wire attached to the mounting bolt. I have 12 volts between the brown wire and the mounting bolt. If I discount the grounding wire (with trailer tounge still on ball, I still read 12V.

As soon as I connect the brown lead !2V wire to the light (which is mounted and now reattached to the grounding wire), the voltage instantly drops to nothing.

Is this a ground, or some weird short. I thought it might be a short so I bought a whole new light package... Same thing. Please note, the 12 running light brown wire is not hooked to anything else. THe other end of the Y is standing free (not hooked to other rear light; side markers are not hooked up).

Hearing from others that the running lights draw more amperage (although this only makes sense if both tail lights are connected and the side markers are connected), I even 'added' and ran a 2nd grounding wire (thicker gauge) back to the same rear mounting bracket; same thing.

Here's what's also strange, If i attach the positive lead of the multimeter to brown 12V lead wire and the negative terminal of the multimeter to the brown lead wire of the mounted light, I read 12 V. Isn't this strange?

I really appreciate any help. Is there a short somewhere within the light? any other things I can do to troubleshoot this with my multimeter?
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Old 09-21-2017, 02:35 PM
walleyeman57 walleyeman57 is offline
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Join Date: May 2015
Boat: mastercraft 1996 prostar LT1
Location: midwest
Posts: 3
I have been fighting lighting issues on my trailer for a couple of years. This year I pulled the tail lights and took a good look. I found that mice ( I assume) had chewed several of the wires which allowed the strands to contact the trailer and thus ground out. This did not cause the 30 amp fuse to blow on the van. It was about 4-5 years ago that I rewired the whole trailer-so its back to square one.
In looking over the damage-the wires that are outside of the boat frame are all fine. The wires enclosed in the trailer box frame is where the chewing occurred. I'm thinking I will rewire again but not fish the wires through the frame and use clips to hold the wires against it. It will not look as nice but the wires being inside of the box frame are protected and the rodents live in there. I will also note that I put mothballs, Bounce fabric softener sheets, and bags of poison inside the boat before storage.
Not sure if this helps-but I thought I would share. My issues were lights that would work intermittently.
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Old 09-28-2017, 09:29 AM
jsturvey's Avatar
jsturvey jsturvey is offline
MC Fanatic
Join Date: Jul 2013
Boat: 1998 MariStar 225VRS
Location: South Central Texas
Posts: 772
^^ Agree. Had the same issue with mine right after I bought it. PO kept boat in a lift at the marina, and the trailer was left in a field to rot for many years. Found many places where mice have gone in and chewed up wiring. I have since had to rebuild and rewire EVERYTHING.

1998 MariStar 225VRS, 350ci LT1

Authorized Dealer for
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