From Basscat discussion - Wiring diagram

Right Turn Green
Left Turn Yellow
Ground White
Tail / Marker Brown (Mine has 2 of these, 1 to each side I assume)Tail lights
Reverse Blue
My issue is nothing at all works. I have verified with truck lights on 12 volts is present on one of the Tail/Marker Brown wires at the plug so I think the plug on the trailer is good at that point. But there is no 12 volts at either tail light.

I don't think this is a ground issue but have not 100% verified this.

When I unplug both tail lights with the trailer plug not plugged in I am seeing 0 ohms across Ground and the Tail/Marker Brown wires on both sides.
I don't think this should be happening.

Any advice.

Are you saying you are removing the bulb and still getting zero ohms?

Ground. Drive around the block and recheck

Try putting a penny on the flat part of the ball and then put the trailer hitch down on to it. If it works, you have a ground issue.

Removing the tail light assembly which includes all bulbs.

I don't see why there would be a short between ground and the wire the supplies voltage to the tail lights.

Try running a separate wire to any of the lights and see if they work that way... That would eliminate the trailer wiring! If you had a direct short somewhere, it should blow a fuse!

Are the running lights disconnected too? Might be reading through those on the brown wire. Take your jumper cables and put them between the trailer frame and truck chassis.

check for a white wire, this is your ground, may have come loose.

power to plug but not lights is normally a ground.

Duh! You have marker lights on each side of the trailer. Those bulbs have elements. Those elements will cause your measured "short" between the tail lead and GND. Unplugging just the tail lights to do a check-for-shorts test is invalid.

When you say NOTHING works then I immediately reach one of two conclusions:

1) Something is wrong on the vehicle, possibly related to isolation circuits for the trailer lamps. If you have verified that you have a live circuit at the connector, then this obviously isn't the case.

2) You have an open connection for the return (GND) circuit.

I opt for #2 as it seems you did do a check on the connector. You have no GND connection for the trailer. Tell me about the white wire on the connector. Is it connected on the vehicle? When you checked for 12V on the brown wire at the truck connector, did you put the - terminal of your test light (or voltmeter) on the connector terminal for the white wire?

On the trailer side, is the white wire connected to the trailer frame? If it is, remove the screw and use sandpaper to clean the ring terminal and the frame, reconnect, test again. If it is not connected, that is your problem. Trailer balls do not make good circuits between truck and trailer frame.

What kind of tow vehicle do you have? I had the same problem with my trailer, been towing it for 8 years with my 08 dodge,come to find out they have a separate trailer fuse.

It is a ground issue. The ground from the connector was screwed to the bottom of the actuator on the swing away tongue. I have ground to the actuator.

I think the overall ground is counting on the main bolt of the swing away tongue to make good contact. I have ground from this bolt all through the trailer but not from the actuator to the tongue bolt. I am going to remove the bolt and clean everything to see what happens.

I may even run another ground wire through from the actuator though the tongue and drill a hole in the frame to attach the ground.[b][/b]

You are on the right track. That bolt for the swing-tongue is a rust magnet that will interrupt GND. Do the jumper to main frame as you described and you won't have any future issues.

Done, Thanks for the advice.

If I was guessing, you have a ground issue.

If you're driving a Dodge Ram 3500 , couldn't get fire to back left stop and blinker lights, something went haywire with fuse box and they have to replace something there EPM or ECM. Should have been a recall but wasn't. They said they (Dodge) have replaced millions on older Dodge trucks.