GM trailer light hookup nightmare.

[Shadow_storm56]

Ok Idk if I'm screwing up or if my dads van connections are bad but he needs me to get the lights on one of his boat trailers working. Should be fairly easy, they are very dim and acting odd, clean up grounds and still dim. Ohh he ran the battery dead testing ok so fix that.... solid tail lights work, left signal all lights turn off right signal both lights blink.... huh? Check wiring..... the tail light circuit is blinking??? That should never happen ok.....

Unhook trailer to check 4 pin output directly with a meter, everything looks correct. Things blinking when supposed to. Test lights themselves, yup high and low for tail lights and blink work perfectly. Pull wires from trailer to see if mice chewed somthing or some weird splice was done.. nope perfectly good wires.

What is happening? Is the system in the van glitching under load? Or am I doing somthing wrong in this incredibly simple setup? Maybe van connections corroded underneath? I'm outta ideas

 

[DustyRusty]

Check the sockets inside of the tail lights on the trailer. Check to make sure that there are no bad grounds with them. When I have problems like this, I use a spare battery to test all the trailer wiring and lighting. Usually it is a faulty ground that is telescoping to all the other lights. I have even had bulbs fail, but they look good. Check the wiring real close because mice like to chew on the wires that are inside of the trailer frame. Also, check the battery cables, and if one of them has a cheater clamp on it, then there is a good chance that the wire has corrosion under the insulation and it should be replaced.
As a side note, yesterday, while watching the Mechum auction there was a high dollar car that had 2 of these type of clamps on the battery, and the "announcer" was saying that the car recently had a high dollar restoration. Guess that they ran out of money when it came to the battery cables.

 

[cliffboyer]

Sounds like van is a 3 wire stop/tail/turn system, and trailer is 2 wire system that combine the stop & turn. A converter will solve that.

 

[bcp]

You can get all kinds of goofy results with bad grounds . Best to have actual ground wires, not just use the trailer frame. Don't ground to the tow vehicle through the hitch ball, either.

As mentioned, if the tow vehicle has separate turn and stop signals, you will need a converter, as most trailers use the same bulb element for both.

Bruce

 

[i7win7]

Best to have actual ground wires, ... Don't ground to the tow vehicle through the hitch ball, either.

If trailer tilts, attach ground wire from hitch frame to tilting section also.

 

[Shadow_storm56]

Sounds like van is a 3 wire stop/tail/turn system, and trailer is 2 wire system that combine the stop & turn. A converter will solve that.

Trailer actually is 3 wire.

 

[Shadow_storm56]

If trailer tilts, attach ground wire from hitch frame to tilting section also.

My ground tested good but it would not be that hard to make it a 4 wire whare the ground is ran the the frame of the light. eliminating the need for ground to pass through the frame. When I say tested good it reads a voltage and a connection,

 

[Daren Todd]

I'm assuming the 3 wires go to power the trailer lights? One for each turn signal, plus one for the parking lights?

Thats usually the case with a 4 flat plug. The white wire just grounds to the trailer frame.

I've had trailer brakes engage when a turn signal or brake lights were engaged. The issue was a bad ground. Ran a separate ground just for the lights and spliced it in at the plug.

Clean grounds. If trailer is really old, then you may be better off to run a ground wire to each light. Especially if the lights are attached to fenders. Years of crud, corrosion, and rust where the fenders attach can cause issues.

As stated before, if it's a tilt trailer, the ground needs to be attached to the deck frame, not the tongue.

If the vehicle is older, grounding was done through the frame. Make sure the ground on the truck side of the plug is good and clean where it attaches to the tow vehicle. Or add in a new ground on that side as well.

 

[Daren Todd]

My ground tested good but it would not be that hard to make it a 4 wire whare the ground is ran the the frame of the light. eliminating the need for ground to pass through the frame. When I say tested good it reads a voltage and a connection,

A test light light has it's uses. A meter will read voltage even if the connection is hinky. A test light will show you how good that connection actually is. I don't use a test light often, but do when I'm questioning the integrity of a circuit.

The brighter the light, the better the connection. If it's really dim, or doesn't light up, your losing voltage some where.

 

[Shadow_storm56]

I'm assuming the 3 wires go to power the trailer lights? One for each turn signal, plus one for the parking lights?

Thats usually the case with a 4 flat plug. The white wire just grounds to the trailer frame.

I've had trailer brakes engage when a turn signal or brake lights were engaged. The issue was a bad ground. Ran a separate ground just for the lights and spliced it in at the plug.

Clean grounds. If trailer is really old, then you may be better off to run a ground wire to each light. Especially if the lights are attached to fenders. Years of crud, corrosion, and rust where the fenders attach can cause issues.

As stated before, if it's a tilt trailer, the ground needs to be attached to the deck frame, not the tongue.

If the vehicle is older, grounding was done through the frame. Make sure the ground on the truck side of the plug is good and clean where it attaches to the tow vehicle. Or add in a new ground on that side as well.

It's quite possible the ground is bad although not a tiling trailer. Does not appear rusty but it's possible. Truck ground and trailer ground have a connection but that does not garentee it is good under load. I will run a ground wire and see what happens.

 

[Lil Foot]

I built a jumper for chasing bad grounds when diagnosing trailer grounding issues.
It's a heavy, but flexible, braided wire, (#8?) with a large alligator clip at one end, small alligator clip at the other, and about 35ft long. I put the large clip directly on the battery minus terminal, then I can touch the other end to various components/wires/junctions/connectors until I isolate the problem area/areas.
I'd post a pic, but just realized it's at my other place.

 

[Shadow_storm56]

I built a jumper for chasing bad grounds when diagnosing trailer grounding issues.
It's a heavy, but flexible, braided wire, (#8?) with a large alligator clip at one end, small alligator clip at the other, and about 35ft long. I put the large clip directly on the battery minus terminal, then I can touch the other end to various components/wires/junctions/connectors until I isolate the problem area/areas.
I'd post a pic, but just realized it's at my other place.

I did somthing similar, I tested it with a separate power supply and the trailers ground and the light worked fine. Hmmmm

 

[Russell King]

I have to assume that the vehicle trailer combination worked together and correctly in the past, but please confirm that. Also please describe the vehicle taillight system, one bulb for turn and one for stop and one for running light or are some combined in one bulb?

I suspect the vehicle may have or need the converter system and if it already has one you may need to inspect the wiring to it. On foreign vehicles that converter was needed to get the trailer to work correctly. They now make those that plugs directly into the wiring harness of the vehicle but in older vehicles they used those blue plastic taps into wires.

If you’re getting into replacement of the trailer wiring look into the wiring harness that is split at the front near the connector. Then you run separate down both sides of the trailer into each light eliminating splices underneath the trailer, much easier to run than the four wires all together (unless you install a weatherproof terminal box at the rear of the trailer

 

[GreensvilleJay]

trailer wiring isn't 'rocket science' AND there is NO '3 wire trailer system'...
sigh
4 wires
White....ground
Brown..running lights
Green..Right Brake/turn
Yellow..Left brake/turn

1st You MUST use the White ground wire ! Anyone who says 'the balls good enough' don't know SQUAT about electrical

2nd use a battery and couple jumpers to CONFIRM the trailer is properly wired

Most problems with dim bulbs is crummy 'grounds', corroded wires.

Since this is a boat trailer, I'll assume it's been in the water once or twice so buy a $25 'trailer light kit' and start from scratch..use new wires and lights. I fix 4-10 trailers every year, have several kits in stock, each trailer gets one. It's faster and cheaper in the long run

 

[dlsmith]

As a side note, yesterday, while watching the Mechum auction there was a high dollar car that had 2 of these type of clamps on the battery, and the "announcer" was saying that the car recently had a high dollar restoration. Guess that they ran out of money when it came to the battery cables.

Any mechanic that uses one of those terminal clamps should have his tools confiscated.
I hate those things. They cause more problems than they fix.

 

[Shadow_storm56]

At the end of the day the van connections were bad. I bought a 7 to 4 pin converter and it works fine. It already had a 4 pin but it was bad. Works great now, I cleaned up the trailer wiring with some nice heat shrink as well

 

[DustyRusty]

Look at this as a learning experience. Sometimes things that are not rocket science need a rocket engineer to figure them out.

 

[Shadow_storm56]

Look at this as a learning experience. Sometimes things that are not rocket science need a rocket engineer to figure them out.

I assumed the van because the tail light circuit was blinking which should be solid. But my dad was so sure it was somthing else. I think it's corrosion as the voltages do read correctly but it can't pas current.

 

[lugbolt]

when I worked at the other place, we sold boats--and trailers along with kubota's. Actually I get calls often from customers that were loyal boat customers wanting side work...anyway....one of the most frustrating things we ran into was trailer wiring and more specifically truck wiring. Oftentimes we'd find that we're getting good power to the trailer but nothing to the back of the trailer once everything was hooked up. Pretty common to find harness problems on pickup trucks, of course we were a kubota dealer and not a car/truck dealer and the boss (not manager, BOSS) said that we ain't fixing nobody's car or truck, so we had to send customers away with either nonworking trailer or leave the trailer at the shop and let them go to a dealer to have their harnesses fixed.

Of those, a large majority were general motors products.

 

[CarleeArnold]

Maybe you can take a look at the wiring diagram for the van to see if something looks off. If all else fails, it might be worth bringing it to a mechanic to have a look and see what they can recommend. It's possible that the age of the current trailer is making it difficult to troubleshoot. Also, it could be worth investing in a new lighting system from reliable retailers, such as truckelectrics.com/pages/lighting. Additionally, have you checked the connections in the van? It's possible that corrosion or a loose connection could be causing the issue. If all else fails, it might be worth bringing it to a mechanic to have a look and see what they can recommend. Whatever you decide to do, it sounds like you've done a great job figuring out the problem so far.