Problems with trailer lights, looking for some help

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Originally Posted by RTRonthefly

I am re-wiring my trailer, and spent the better part of the weekend scratching my head as to what the problem could be.

I have a new LED light set and trailer harness (4pin) from Princess Auto. I got everything installed, connected and found some very dim lights when connected to the car. I checked and cleaned all the grounds. There is a ground at the hitch harness & each light has a ground. Still very dim lights. I double checked all grounds and all connections & still dim lights. I took the lights off and tested them to my battery & and they actually are quite bright.

So, I grabbed the multi-meter and did some checking.

I turned the car on, turned the lights on & checked the voltage out of the curt harness = 11.8v

I then hooked up the trailer's harness and checked the voltage at the back of the trailer with bare wire (I had pulled the lights off previously). I got 11.1v at the rear. I then twisted all my wires together and attached my ground - and measured 5v with dim lights... Not sure what the problem may be.

Any thoughts/suggestions?

thanks
RTR

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If you're only getting 11.8 volts from the trailer plug at your vehicle with it running, you have a problem wit the vehicle wiring. While running you should see at least 12.5 to 13 volts at the trailer plug.

Fisherman, sorry the car wasn't running, just key in turned to the halfway position & then turned the lights on.

Just did a quick check - 13.8v off the harness with the car running..

Still sounds like a bad ground or bad connection (Crimp??)

I drove myself three-quarters insane with my boat trailer,last summer, until my electrician neighbor suggested grounding each light,individually,to the trailer frame. I attached a wire from the outside mounting bolt to a small bolt on the frame. It's worked like a charm with no issues,ever since.

I think we have a winner, and thanks to all on the forum for the help and advice!!!

I created some test wires/terminal rings and started to test the grounds with the multi meter measuring resistance.

The ground I used at the lights measured 40.0+ so I figured I had a bad ground. To confirm I hooked up a few wires and ran my ground all the way back to the tongue hitch. Sure enough the lights are now 10x brighter than before. I think I need to run my grounds from the lights back up the frame closer to the hitch.

With LEDs, you may get away with a poor ground for a little longer, but sooner or later that poor ground will become NO GROUND.
When wiring a trailer, there are three rules. #1-you can connect your harness ground to the tonque at the front ( coupler), but you should also run it right back to the light fixture. It's only one extra wire and will cost maybe $1.00.
#2- Solder EVERY connection! There are two kinds of connectors normally used around trailers. One is a squeeze on type that cuts through the insulation and half of the wire strands. They work for a few months or until they get wet (or salty). The other type, that you strip the wire and then squeeze on with a special pair of pliers, work a little longer but still start to deteriorate when they get wet.
#3- Try to keep all joints as dry as possible. Water will not short out a 12volt system but it will cause the copper to corrode and turn black from copper oxide. That thin black layer is an insulator.....
You can buy liquid rubber at Home Hardware in a small yellow tin for a few dollars that is designed to seal your connections. Put on a few coats then store the tin in the back of the fridge as it has a short shelf life once opened. Any connections that you do not solder, such as light bulbs and plugs should be coated in grease, NOT WD40......

There is another way to ensure good solid, multi year, electrical connections with boat/trailer connectors. There is available "dual wall" connectors ( butts, rings, fork etc ) that are "dimple crimped" on, then heat gun or lighter flame to melt the silicone interior of the connector. This make a water proof, air tight connection. The exterior of the connector is nylon and the interior is silicone...works like a charm.

Continuing on the "sealing wire connections"... I've used a dual-layer heat shrink before... looks like typical heat shrink but the inner layer is a low-melt adhesive. Think 'hot glue'. As you heat it the inner layer melts and the outer layer shrinks... squeezes into the connection and seals to the wires.

The last trailer I did I decided that darn dual-layer heat shrink was too expensive... so I used regular heat shrink and a hot glue gun. Dab of hot glue on the soldered joint, let it harden up a bit, slide heat shrink over, heat it up with a heat gun. The low-melt glue (arts and crafts stuff) would melt easily.

I also solder all my connections. Adds time, but makes for a much better connection.

The majority of trailer wiring problems I see are grounds or bad connectors.

All good advice so far.What I have found and yes think it has all been said in here somewhere at least once:-)LOL
1.Readings with a meter are only a guide.They can show if a connection or fuse ect is totally gone.But a weak or dirty one will conduct well enough for a meter.Put a load on in like the light and if the voltage goes down you have problems.Try and always read the meter with a load on the circuit.
2.Cut your search in half by trying a light right at your truck harness immediately.And check it with a volt meter first.That will tell you if the problem is at the truck end or in the trailer.Most times it is in the trailer but the one time you assume just because the meter said it was fine at the harness.....:-(You will kill yourself for hours on a perfectly good trailer.
3.A good spray spray spring and fall of all conenctions,sockets,bulbs with a good electrical non conductive corrosion proof spray works wonders.
4.Disconnect the harness when it's under water even if it's supposed to be "one of those great sealed systems that doesn't require it"....
5.Run a ground and most problems are with the ground.Don't use the chassis ground alone.To much problem with dirt and corrosion.Even if you are diligent with dialectric grease and such.
6.Use no crimp connections of any kind.A marrette filled with silicon works better.Solder the works.And silicon and heat shrink,rubber and electrical tape over all connnections afterwards for added protection.
7.New,larger guage wire front to back.And wrap it with cable wrap for mechanical protection.
8.Everything is fused seperate at the truck now.Which can add to assumtions and confusions if one side or the truck lights are working fine.The trailer and each side and the low and high elements are fused seperately.
9.Avoid any connection or splice that you can.
10.If a visual doesn't point out the problem early.Just work your way back along the harness to find it.Take a light along with you that you "know works".Along with the volt meter to check.

If you miss the problem anywhere the first time by.You will spend hours and hours needlessly aftre that once you think a section or componenent is fine.So a quick double check of things can be invaluable.
Think thats it.Lol.

I found once I ran a new harness front to back like this I never had a problem.Nothing worse then always tinkering with them...

Cheers!

All good info. Here is a bit more.

First things first, ensure all the correct signals are coming off the truck. I have seen guys drove just about nuts chasing a trailer light, when it was never going out of the connector on the truck.

You will have better luck with a test light than a meter. The chassis ground will sometimes not read the DVM, but the test light provides a solid ground.

When grounding, grind off the paint or finish, use a star washer, self tapper or bolt, the repaint or protect the newly ground spot.

Solder everything, use heat shrink. Crimp on, twisting or tapping is just a recipe for corrosion.

Try to run single runs of wire all the way back, any splice will cause a potential fault.

Don't over think it. Start with known good, ie the truck, and start to work back from there. The theory is bone- simple, patience and attention to detail, will prevail.

Good luck..