ColdBrew

Trailer lights driving me crazy

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Hi gang,

I have a problem with the lights on my clamshell. The right brake light and directional will not work. I've checked all the lights and all the grounds and I can't seem to find the problem. I'm considering removing the grounds behind the front marker lights and redoing them, but I figured I'd ask before I went through the hassle. 

What I've done so far is:

replaced the light unit (just in case)

removed all the lights on the trailer to check grounds and connections

Replaced the plug that goes to the truck

swore loudly and kicked the trailer ( didn't help)

One symptom that it has is that the lights on the right side DIMMLY blink a little when I have the LEFT directional on.

 

Thanks for any help,

Dave

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Trailer lights can be a real PIA to troubleshoot. As @Yamiblue said, make sure the plug on the tow vehicle is working correctly first.

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I'm with Yamiblue. First thing is "do you have a multimeter?", and, if so, have you checked the voltages at the truck's connector? (They sell an LED gadget that plugs into the truck connector to test this but you don't need that) Read the voltages between the ground pin and the three pins used for left & right directional/brake lights and the pin for tail/marker lights. 

What type of connector do you have on your truck? is it a 4-wire connector or do you go through a converter to create a 4-wire connection? I've had the converter go bad. Where you're having additional lights come on when the left directional is on says there's a connection between wires somewhere. Of course, a quick test for the truck is to hook another trailer up to it.

Your trailer wiring (4-wire)should be Brown-tail/marker Green- right turn/brake Yellow- left turn/brake White-ground. Verify that you have 12VDC at the proper pins at the truck connector.

Now, with the trailer wiring disconnected from the truck, take your multimeter and check for the connection between the trailer's wires. With the setting on the meter set to Ohms look for a low reading between the White (ground) wire and the other 3 wires. Remember that you're reading through the wires and the light bulbs. If the yellow, green, or brown wires show a direct short to the white wire (zero ohms) that wire is touching the trailer frame or the white (ground) wire. If any of the yellow, green, or brown wires show an open with the white wire you have a bad connection, broken wire, or a defective bulb. Measure resistance between yellow brown and green wires, there should be an open, no connection, between the wires.

 

 

 

Edited by jhwentworth

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If chaffing was the issue, wouldn’t be a bad idea to run all trailer wiring in some wire loom if it’s not already done this way. This could help minimize any future chaffing of wires

 

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I've also seen a combo battery pack and tester some dealers have for diagnosing trailer light issues.

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We can count out the truck. This is a new truck this season and I had the same problem in my old truck. Also....my boat trailer is fine. Everything else might be over my head, but maybe I can borrow a multi-tester and give it a shot. Thanks for the ideas.

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You can buy a digital multimeter for $10-$15 (Walmart) that will get the job done. Without a meter you're just guessing. We used to call that troubleshooting style "shotgunning" or "swap 'til you drop." It can get expensive doing it that way if you don't get lucky.

Get a meter and we can probably walk you through it.

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I've had problems with mice getting into the trailer frame during the summer, where the wires run through. They love to eat the insulation, causing a short somewhere between the front and back. I wound up buying a complete wiring kit (at Wal-Mart I think), and replaced everything. It wasn't hard to do. Took the old wires out, they had eaten the insulation for several feet. so the bare wire was touching the frame. That can cause your problem where a different light comes on dim. 

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21 hours ago, ColdBrew said:

.......One symptom that it has is that the lights on the right side DIMMLY blink a little when I have the LEFT directional on.

You definitely have a ground issue. The symptom above shows that. The right side lights may be solidly grounded to your frame, but there probably is a problem between that portion of the frame and up near the tongue where you have the plug grounded to the front of the frame. Its a hassle, but when I rewire a trailer I never ground to the frame, especially with clamshells, but actually run a ground wire all the way back to the rear lights, and always make sure I place a ground strap on the shell to the frame. On a side-note, a lot of light issues on the clamshell itself is due to the fact that many manufacturers don't run a separate ground wire or strap between the clamshell and the frame below.

One way to isolate the issue would be to run a temporary ground wire from the front of your frame where the plug now grounds to right near the rear of the frame where your left tail light is grounded.

Is this a wishbone frame?. Lots of times corrosion will form between the sections of that type of frame interfering with a good ground path from the tongue area to the rear of the trailer.

 

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6 minutes ago, Skip said:

You definitely have a ground issue. The symptom above shows that. The right side lights may be solidly grounded to your frame, but there probably is a problem between that portion of the frame and up near the tongue where you have the plug grounded to the front of the frame. Its a hassle, but when I rewire a trailer I never ground to the frame, especially with clamshells, but actually run a ground wire all the way back to the rear lights, and always make sure I place a ground strap on the shell to the frame. On a side-note, a lot of light issues on the clamshell itself is due to the fact that many manufacturers don't run a separate ground wire or strap between the clamshell and the frame below.

One way to isolate the issue would be to run a temporary ground wire from the front of your frame where the plug now grounds to right near the rear of the frame where your left tail light is grounded.

Is this a wishbone frame?. Lots of times corrosion will form between the sections of that type of frame interfering with a good ground path from the tongue area to the rear of the trailer.

 

X2 on what Skip said, I also run a separate ground from each light to the front (one common grounding point). That dimmly flashing light shows the trailer searching for a ground.

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Quote

One way to isolate the issue would be to run a temporary ground wire from the front of your frame where the plug now grounds to right near the rear of the frame where your left tail light is grounded.

Where is the first grounding point suppose to be at the front of the trailer? I assumed it was the ones behind the running lights. Is there suppose to be one before those?

Skip. This is a wishbone frame.

Edited by ColdBrew

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Often times, the ground wire in the trailer side is only a couple of feet long, and is attached to the frame up front. The entire trailer frame becomes the ground 'wire'. As said above, if there is some corrosion between the parts (wishbone and frame), the back half won't be grounded. 

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Be sure to use dielectric grease on all connections. Fluid Film is also a good alternative

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2 hours ago, ColdBrew said:

 

 

Where is the first grounding point suppose to be at the front of the trailer? I assumed it was the ones behind the running lights. Is there suppose to be one before those?

Skip. This is a wishbone frame.

Look at your trailer side harness wiring. You’ll find that the ground wire is screwed into the frame somewhere within a few feet of the trailer tongue. Because you have a wishbone trailer, and one side of your trailer lights work while the other side is bavkfeeding further convinces me that frame corrosion has interrupted the ground path. Somewhere near the tongue of your trailer run a ground wire from that part of the frame back to the frame near your bac light assembly. Tack (screw) both ends of this wire into the frame and I’ll but you a beer if this doesn’t fix the poroblem!

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As stated, certainly sounds like a ground issue. Scrutinize any butt connectors and wiring for damage. I've seen many times people poke holes with test lights or even worse use scotch clips. 

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23 hours ago, Skip said:

Look at your trailer side harness wiring. You’ll find that the ground wire is screwed into the frame somewhere within a few feet of the trailer tongue. Because you have a wishbone trailer, and one side of your trailer lights work while the other side is bavkfeeding further convinces me that frame corrosion has interrupted the ground path. Somewhere near the tongue of your trailer run a ground wire from that part of the frame back to the frame near your bac light assembly. Tack (screw) both ends of this wire into the frame and I’ll but you a beer if this doesn’t fix the poroblem!

As much as I want that beer, I hope you're right. I'll give it a try this weekend. Won't have time before then. Thanks to all for the help! 

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So while I was out yesterday I purchased a replacement for one of the small round "running" lights on my trailer. I know it was just burned out because I switched it with another one just to make sure. After I replaced it.......THE DAMN DIRECTIONAL WORKS!!??

I'm not complaining, but geez. Is this thing that sensitive that a burned out light messes with other stuff?

Thanks again for all the help on here. Hopefully this solves my problem for good.

Dave

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Glad you got it figured out...treat yourself to a beer! 

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2 hours ago, ColdBrew said:

So while I was out yesterday I purchased a replacement for one of the small round "running" lights on my trailer. I know it was just burned out because I switched it with another one just to make sure. After I replaced it.......THE DAMN DIRECTIONAL WORKS!!??

I'm not complaining, but geez. Is this thing that sensitive that a burned out light messes with other stuff?

Thanks again for all the help on here. Hopefully this solves my problem for good.

Dave

A simple burned out single filament bulb shouldn't bother other circuits. In two filament bulbs, if the ground connection is lost between the metal bulb case and the external ground circuit, electric current can flow between the brake/directional  circuit and the taillight/running light circuit. (the brake and tailight filaments share a common ground point inside the bulb.) That can't happen in a single filament bulb. Typical electrical resistance readings (ohms) for a snowmobile trailer should be about 2 ohms between the ground wire (white) and the brown, yellow, and green wires. With the bulbs installed you'll see about 2 ohms between the brown, yellow, and green wires. As the running lights are (usually) single filament bulbs, if the two rear brake light/tail light bulbs are removed the chances of this electrical backfeeding  should be remote. You can remove these two bulbs one-at-a -time to troubleshoot grounding problems.

 

If you get deep into a grounding problem remember that there are three sources for a trailer ground: The white wire in the trailer connector, the trailer ball, and the safety chains. The last two are not reliable ground connections.

Edited by jhwentworth

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Probably wiggled a connection, is the round light near the previously problem light? 

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Not originally. I have a total of 5 of those round lights on the back of my trailer. 1 on each end and 3 in the center. The middle one in the center is the one that was burned out, but I took the one from the right corner (problem side) and replaced the one that was out to make sure it was the light and not just a bad connection so maybe you're right.

Either way....I'm just happy to see it working. I want to sit out there for a few hours some night and just watch it blink.......:D

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