Boat Trailer Lights

[waldreps]

I need some help diagnosing my boat trailer light problem. First, the symptoms. When either turn signal is turned on, both trailer lights blink. When the brakes are on, both trailer lights go out. When just the tail lights are on, both trailer lights are on as they should be. I thought it may be a bad ground so in an attempt to fix the problem, I ran a ground wire from the harness back to each trailer light. I also tested my vehicle plug and everything tested good there. The ground wire didn't help. I used my test light while just the tail lights were on and the stop/turn wire on the inside of each trailer light weakly lit the light. Does this indicate a short somewhere? When the brakes and turn signals are off, the green and yellow wires shouldn't light the test light at all, correct? Any suggestions would be greatly appreciated.

 

[series9]

A friend brought by his trailer this week with light problems. He had "cleaned" the plug with WD40 and that was causing a short.

Did the lights previously work correctly?

 

[series9]

Trailer lights are generally junk.

I have solved most of my problems by installing LED submersibles, because they require lower current to operate correctly. I also ran an actual ground wire to the back, instead of relying on the trailer itself to conduct the current.

The plugs are also junk. I cut mine off and installed Weatherpak connectors, and that has been helpful as well.

 

[waldreps]

At one time the lights worked but I've had the boat in the garage for a year or so while I was working on the motor. I can't afford to switch to LED lights as this is just a really old boat and trailer and not really worth much investment. I just want the lights to work to be legal. I'll try cleaning the connector with electrical cleaner and see if that does anything. Otherwise, I'm thinking that if I'm getting a faint light on my test light when I touch it to the stop/turn wires when only the tail lights are on, then I think I have a short somewhere. Does that sound right?

 

[UncleWillie]

The Tail lights are cross feeding into the Turn/Brake lights.
The Tail lights and the Turn/Brake lights are two separate Filaments inside of a common bulb. xx57 Series Bulbs

Both filaments share the same ground in the bulb and the light fixture.
If the Tail Light power can not find a solid Ground Path, it will find a path through, and dimly illuminate, the other, Brake/Tail, Filament.
The power goes in the TailLights and comes back out the Brake/Turn Light instead of going to ground.
Weird thing happen when you power both sides, the light go out, when you expect them to go on. Poltergeists?
This is a very common failure that confuses many people. <---<<<
You have a Bad Ground Connection(s) in the Tail Light fixture(s).
You have an OPEN... Shorts cause Fires. Opens cause frustration.
WD-40 does not cause shorts. Spray away as you please!

Be sure you understand why you are replacing a part before you start throwing money at the wrong problem.
Remember it worked before, it will work again without blindly replacing everything because you do not understand the problem.

*** Hint: When it absolutely makes no sense, and it appears that magic is at play; it is a Ground Problem!

 

[Tater72958]

You can get a set of led trailer lights for about $25 off the web. Maybe cheaper.
I put leds on all my trailers. I havnt touched them in years.
And they are so much brighter. When backing up at night just lightly touch the brake pedal and BAM!! You can see

 

[waldreps]

UncleWillie, I ran a separate ground wire to each trailer light all the way from the ground wire of the harness. If I still have a bad ground, then a good ground isn't possible for me...lol. I'm guessing it must be an open then. Would an open cause both lights to go off when I press the brakes? Tater, I'll check on an LED setup but I really want to figure out what's going on first.

 

[bruceb58]

You may have grounds from the lights to the harness but you aren't getting a good ground from the harness to the vehicle.

 

[waldreps]

bruceb58, I think that's the case cause I just discovered that when the trailer is connected to the vehicle via the hitch, all the lights work fine. If I wiggle the trailer though, the lights blink. My problem is how do I get the ground in the 4-way plug to work properly. I tested the vehicles 4-way plug and it tests good. The trailer 4-way plug is relatively new and the ground wire connects to the wires I ran to the lights. Is one of the 4-way plugs bad? If so, which one? They both seem like they should be fine. I don't want to have to run another ground wire from the trailer to the vehicle but I don't see any other way to fix it since the ground in the 4-way plug isn't doing its job.

 

[MTboatguy]

Normally when I wire one up, I run the ground from the plug to a stub on the trailer and use a self tapping screw, in other words, I secure the white wire out of the plug to the trailer to the frame and then on the lights, I secure the grounds on the lights to the frame of the trailer as well, that way the whole trailer becomes a ground, I also use dielectric grease on all of my connections and if I have to splice a wire, I use shrink wrap butt connections, I also use dielectric grease on the bulb sockets and make sure the lights are sealed as well as I possibly can make them. If the truck is what is giving you the problem, then you need to crawl under it and figure out which wire is the ground wire and stub it off and attach to the frame on the truck so you know you have a good ground. I also keep both truck and trailer ends in my tool box, and carry a full electrical kit with me at all times, that way I can repair things on the road. Worse comes to worse, I also have a set of magnetic LED lights with me in a tool case, so if all else fails, I plug them in and a put them on the trailer. They get real nasty about lights where I live.

If you see white power on any of your connections clean it and then apply dielectric grease.

 

[GA_Boater]

Check the white wire from the car/truck plug to where it is tied to ground. Loose or corroded is my guess.

 

[series9]

A full LED kit, with wiring and connector at Lowes is only $45. You've already spent $45 of time on it.

 

[bruceb58]

LED kit isn't going to work either if he doesn't have a ground connection to his vehicle.

 

[MTboatguy]

LED kit isn't going to work either if he doesn't have a ground connection to his vehicle.

Exactly, it ain't going to work, no matter what it is, if you don't have the electrical working right.

 

[UncleWillie]

Turn ON the Head/Tail Lights of the truck.
With a Test lamp or Meter, measure between Truck Connector BROWN and Bare Metal of the Truck. 12v?
Measure between Truck Connector BROWN(Pin #2) and Truck Connector WHITE(Pin #1). 12v?

With the Trailer OFF the Ball... Connect Truck and Trailer Connetors together. Tail lights ON, even dim?
Measure between Connector BROWN and Trailer Connector WHITE. 12v?
Measure between Connector BROWN and Trailer Frame Bare Metal. 12v?
When did you loose 12v?

Trailer still OFF the Ball...
Measure between Truck Bare metal and Trailer Bare Metal. Zero Volts?

This is going to be a 10 cent fix. There is no need to spend any money at this point!

 

[UncleWillie]

UncleWillie, I ran a separate ground wire to each trailer light all the way from the ground wire of the harness. If I still have a bad ground, then a good ground isn't possible for me...lol. I'm guessing it must be an open then. Would an open cause both lights to go off when I press the brakes? ...

You have not identified a good ground in the trailer yet.
When you ran the wire, where EXACTLY was it run. The White connector wire, The lug on the end of the wire? The bolt the lugs is attached to? The frame next to the Bolt? These are all different, Untested, ground points.
The wire went to the the trailer light ground..... The Ground at the actual Bulb? The Ground in the lamp socket? The Metal base of the light fixture? The White Wire of the Light Fixture? The Lug on the end of the wire? The bolt the Lug is attached to? These are all different, Untested, ground points.

The devil in in the details. You must be very specific when trouble shooting.
Assume absolutely NOTHING is connect to ANYTHING, no matter how obvious, until you confirm that they actually are.

And, Yes! An OPEN GROUND will cause The Tail Lights to go out when you press the Brakes. Read Post #5 again!

And Again: When it absolutely makes no sense, and it appears that magic is at play; it is a Ground Problem!

 

[MTboatguy]

You really need to read UncleWillie's posts over and over again, they have you on the right path to success.

 

[waldreps]

Ok, I figured it out. Even though my testing of the truck 4-way plug showed it was fine, the problem was with the truck. The white ground wire from the truck isn't getting a good enough ground to work right. Apparently it's enough to test fine but not enough to make the trailer lights work right. I used a multimeter and test light to test the truck and trailer wiring and everything appeared to be fine until I tested for continuity from the ground terminal of the truck 4-way plug to the frame of the truck. It was in the 1000 Ohm range so it was getting some ground but not good. I don't know why it's not getting a good ground cause it runs into the vehicle harness to other parts of the truck. So, I just spliced into the wire and grounded it to a bolt on the frame. Now, all my trailer lights work whether the trailer is hitched to the truck or not. Thanks for all of the suggestions.

 

[Tater72958]

Im thinking its in the truck. What model truck you got? Some trucks have a plug the is in the frame rail. You might check it out. Unplug it and pug it back in. But you should really run a ground wire from you truck 4pin plug to a good ground on your truck somewhere.

 

[MTboatguy]

Glad to hear you got it working, I never depend on the factory wiring for the ground system when it comes to trucks or cars, I always pull their ground wire and wire it directly to the frame.


Now at least you will be able to tow and enjoy your summer.