Trailer light problem

[rexmitchell]

I've searched and looked at at least 15 threads but nothing with the exact problem I'm having. Here is the story of events. Right running light goes out, turn signals/brake lights/side lights/left running light still working. Right bulb terminal is toast but is still working for the brake light/turn signal(it will have to be replaced but thats not my problem I don't think). After getting a new bulb in the right, now the left running light (along with the right) and side running lights no longer work, both brakes and turn signals do though. I checked the connecting wires, and my extension was bad so I replaced. Still nothing. I checked the ground, its good and I checked my truck harness and fuses, all good. I'm stumped because one: the left light was working and now stopped, and two: because I can't seem to find any wiring that is torn up or loose. Do the running lights work in sequence so that if one is bad they both are? I can't figure out what happened between the time the right bulb was replaced and the left light going out. Could the right terminal impact the left? As I said before, the right will have to be replaced but is that what is causing the left to not work?

Thanks, Rex.

 

[Thalasso]

Re: Trailer light problem

 

[glenn property of pam]

Re: Trailer light problem

sounds like a blown fuse on the tow vehicle test voltage between brown wire terminal and ground. Some modern vehicle will shut off power if they sense a hard short to ground so you might have to unwire the brown wire from the bad light socket as well as side you just replaced to see if that is causing the problem.

 

[rexmitchell]

Re: Trailer light problem

Thanks, I'm aware of how it is wired.

sounds like a blown fuse on the tow vehicle test voltage between brown wire terminal and ground. Some modern vehicle will shut off power if they sense a hard short to ground so you might have to unwire the brown wire from the bad light socket as well as side you just replaced to see if that is causing the problem.

Checked the fuses and I checked at the trailer connection, all is well. The truck wiring is good.

 

[glenn property of pam]

Re: Trailer light problem

ok so you have 12v at the brown wire so just plug the trailer in and pull the bulb out then measure the pin in the base to the outside and see if you have 12v when the trailer is plugged in. All the items that do not work are on the same brown wire and as the brake lights work that proves the ground is good.

 

[stylesabu]

Re: Trailer light problem

ok doesn't make alot of sence,but that usually means ground issues. is your trailer bolted or welded,bolted have more ground issues. I but waterproof led lights on mine 2 years ago have worked every since. i bulb type sockets are always a pain. do you know how to use a voly meter and check voltage drop?

 

[Silvertip]

Re: Trailer light problem

You do realize #1034 and #1157 bulbs are keyed so they only go into the socket one way don't you? If you forced the bulb into the socket in the wrong orientation you can very easily come up with the problems you are having. Hold the bulb in front of you so the little nubs point right and left. Notice that one is higher than the other. That's the key! The socket is made with the slots offset but they are made so poorly you can force the bulbs in wrong.

 

[BF]

Re: Trailer light problem

A good rule of thumb is, when funny things happen with trailer lights.... it's pretty much always a bad ground. Bad grounding can come from 1) not having a good dedicated ground wire that is bolted to the trailer tongue which means you end up relying instead on the hitch connection between the trailer and tow vehicle to act as the ground, 2) not having good ground path that bypasses pivot points of tilting trailers (don't expect the frame on one side a pivot point to be electrically connected to the other side of the pivot point unless you bolt a wire to both pieces) or 3) poor/corroded ground connections between lights and the frame (you may want to run a dedicated ground wire to each light).

good luck

 

[GeneH]

Re: Trailer light problem

Rex, why not go ahead and replace the right since it is going to have to be done anyway and see what you have then? I would fix anything in the system that I know is bad before troubleshooting the whole thing. I agree that bad grounds are often the problem. I sometimes use a jumper cable to verify ground between the truck and trailer and don't forget the ground between the light assembly and the trailer. This is a problem area too.

 

[rexmitchell]

Re: Trailer light problem

A good rule of thumb is, when funny things happen with trailer lights.... it's pretty much always a bad ground. Bad grounding can come from 1) not having a good dedicated ground wire that is bolted to the trailer tongue which means you end up relying instead on the hitch connection between the trailer and tow vehicle to act as the ground, 2) not having good ground path that bypasses pivot points of tilting trailers (don't expect the frame on one side a pivot point to be electrically connected to the other side of the pivot point unless you bolt a wire to both pieces) or 3) poor/corroded ground connections between lights and the frame (you may want to run a dedicated ground wire to each light).

good luck

We have a winner (although I figured it out before I read this ) I have a ground bolted to the frame of the trailer, however I wasn't hooking the trailer up to the truck when I was testing everything, just connecting the harness. As soon as I hooked it up to the trailer, all lights except the right rear are working again .

Rex, why not go ahead and replace the right since it is going to have to be done anyway and see what you have then? I would fix anything in the system that I know is bad before troubleshooting the whole thing. I agree that bad grounds are often the problem. I sometimes use a jumper cable to verify ground between the truck and trailer and don't forget the ground between the light assembly and the trailer. This is a problem area too.

Light is going to be replaced, I was just stumped as to what else had happened. I am going to pick a new light up tomorrow and hopefully get it installed by tomorrow night. Now that the rest of the problems are solved I'm in a way better mood.

 

[NYBo]

Re: Trailer light problem

I have a ground bolted to the frame of the trailer, however I wasn't hooking the trailer up to the truck when I was testing everything, just connecting the harness. As soon as I hooked it up to the trailer, all lights except the right rear are working again .


...Now that the rest of the problems are solved I'm in a way better mood.

Your ground problem is NOT solved. The lights should work fine with just the harness connected. Since you apparently have a proper ground on the trailer side, it sounds like the white wire on the truck side isn't properly grounded.

 

[rexmitchell]

Re: Trailer light problem

The trailer wiring checks out on the tester, so I'm not sure how that is the issue. My other trailer works fine unhooked as well

 

[NYBo]

Re: Trailer light problem

The trailer wiring checks out on the tester, so I'm not sure how that is the issue. My other trailer works fine unhooked as well

Then I must have misinterpreted your post. Do the lights work with just the wiring harness connected to the tow vehicle, i.e. without being hitched? In other words, what do you mean by, "I wasn't hooking the trailer up to the truck when I was testing everything, just connecting the harness."

 

[rexmitchell]

Re: Trailer light problem

Yes on my boat trailer the lights only worked when the hitch was on the ball and the lights were plugged in. I have an enclosed trailer that I tested my truck on and the lights worked without being on the hitch.

 

[glenn property of pam]

Re: Trailer light problem

Yes on my boat trailer the lights only worked when the hitch was on the ball and the lights were plugged in. I have an enclosed trailer that I tested my truck on and the lights worked without being on the hitch.

That's because the boat trailer has a bad ground and the enclosed trailer does not. Fix the ground on the trailer as the ball is not meant to be the ground return.

 

[rexmitchell]

Re: Trailer light problem

Ok I hear you. The ground is good on the trailer. Bolted down good, all clean, and the wires are intact unless they have corroded inside and I can't see it. I went over all the wiring and everything looks remarkably good except the right rear housing and light.

 

[NYBo]

Re: Trailer light problem

That's because the boat trailer has a bad ground and the enclosed trailer does not. Fix the ground on the trailer as the ball is not meant to be the ground return.

^This.

 

[BF]

Re: Trailer light problem

Ok I hear you. The ground is good on the trailer. Bolted down good, all clean, and the wires are intact unless they have corroded inside and I can't see it. I went over all the wiring and everything looks remarkably good except the right rear housing and light.

The ground is NOT good on the boat trailer. It appears to be good, but it is not functioning as a ground (and therefore is bad). Yes, it's probably a broken wire within the insulation. Grounding through the hitch connection is not good. Goofy things will continue until you fix it... maybe not sitting in your driveway, but once you get some shaking of the hitch connection, or a bit more rust on the ball that secondary ground will fail and the whackyness will start up again. You've diagnosed the problem, now you just need to fix it.

 

[kenmyfam]

Re: Trailer light problem

Top 3 reasons for trailer light issues.

1. Bad ground
2. Bad ground
3. Bad ground

The trick is finding it. Good Luck and even consider replacing the ground wire or adding one.