Problems with trailer lights, looking for some help

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

Do you have a tilt trailer? Mine had a poor ground (frame) connection between the back of the trailer and the tongue.

Maximus,

Would that still be possible after confirming the voltage at the rear, using the bare harness wires and grounding to the frame with the neg probe of multi meter?

Did I write this??? I just went through the exact same deal with my utility trailer 2 weeks ago and finally said, "Screw It"!
Some would work one day then others would work on a different day. I think my problem was with those pinch type connectors (not the butt connectors) that commercial trailer makers use but I got so frustrated I just gave up.
With your issue, dim lights sound like its a poor ground some where in the one of the lines.

The worst thing is is that there's nothing simpler or more basic than trailer wiring.

Sounds like something is connected in series...
Try connecting one light at a time.. And see what happens.

I guess my question is - if I test the bare wires at the back of the trailer and use my multi meter probe to touch to my grounding spot and get a reading of 11.1v, is that proof of a good ground?

Else I wonder if this could be related to my fulton hinge tongue? I have grounded the main harness by the hitch, but the grounds for the lights are at the rear (ie. behind the cut I made to split my trailer in 2).

Thoughts?
RTR

Your ground is fine.

Try connecting one light.. See what happens.. Then connect the next light.

Another approach is to measure resistance from the ground plug terminal on the tongue of your trailer to the frame ground near your lights. If it measures anything more than 0 OHMS you have a corrosion / bad ground wire connection. The same can be said with the hot / 12 volt wire going to the light. You can simply check this with the trailer unplugged from the tow vehicle.

Sounds like the ground to me too.... Try lighting each bulb on the trailer using the plug only.... Don't hook it up to the truck...get a battery and ground the negative right to the frame of the trailer then attach the power wire to the wire for the left, right and clearance lights.. one at a time with alligator clips.
keep in mind for a light to work it needs a good ground and a positive, hook up a positive directly to the wire (example right signal) hook up the negative right to the ground trailer plug wire and see if it's bright, if its not hook up the group to the trailer and then see if its bright... then if that fails too, hook up the ground directly onto the ground on the light itself... Trailer lights are easy if you don't over think it... All lights need a positive and negative in order for it to turn on, sounds like your ground is not making a proper connection to the light bulb itself... take ;your time and using a test light will help determine if the power and ground is getting there (each light) properly... Do your testing one light at a time, once you find the problem with one light, I am sure all the others will work too...
Good luck