Well, it's been a minute since I had one of the these, but here goes. We completely rewired one of my belly dump trailers this winter. From the socket to every single light, everything new. Hooked up a truck today, if it matters it's a 2000 Freightliner FLD112. Checking lights, and discovered that the 4-ways or the right turn cause the turn signal circuit breaker to trip after about 5-6 flashes. Unplugged trailer, works just fine. Removed all turn signal lights from the trailer, still breaks. Pulled the boot off the socket, disconnected green (right turn) wire. Still breaks. Unplug light cord from socket, no problem. This is a brand new Grote socket. Pulled another truck and trailer around, went to the parts room and found a brand new light cord. Plugged the problem trailer into the second truck, lights work fine. Swapped, so the Freightliner was powering the second trailer, everything is fine. The only thing that is weird is the 4" round LED taillight only lights the two center dots when it flashes those 5-6 times before the breaker lets go. Same light works perfectly with the other truck connected. I have checked resistance between the green and ground with the lights unplugged, nothing. I've compared resistance between the left side circuit and the right side circuits with the green or yellow wires connected together at the lights, and measuring at the socket. Both an identical 0.1 ohms. The only thing I have left to try is swap out the socket for another. You can't make this **** up.
Well, thanks to everyone's help, I figured out the problem, lol. This morning, I decided I would bypass the socket on the front of the trailer, and attempt to see what would happen if I connected the ground and green directly to the male plug on the end of the cord. As soon as I touched the ground wire to the plug, I had a spark. This is the ground wire from the trailer harness, mind you. So, take the meter, and I discover that if I put the black on the ground in the truck light cord, and the red to the trailer frame, ground, whatever, I get voltage that matches the turn signal pulses. Now I'm really stumped. Luckily for me, I decided to unplug the auxiliary cord that operates the gates, and everything is as it should be. After a little more diagnosing, I find that the auxiliary cord is sending pulses of voltage through the ground conductor. Come to find out that in searching for a ground for the auxiliary cord, it was attached to a terminal in the circuit panel that was ground, until you turned on the right turn signal, and at that point it became the right turn signal. I did not investigate any further, I will assume it showed ground because the lights in the right turn circuit are connected to ground. Unhooked the misconnected ground wire, found a suitable ground, and we are in business.
I had a 345 cat hoe with a similar problem. They complained that it had repeated starter solenoid failures. I found that in the relay box behind the cab someone had run the boom lights ground wire onto the starter solenoid power supply terminal so every time the lights were on it was also powering the start solenoid with low voltage power after going through the light “ resistors”.
So, what led you to find it?
I was checking the Voltage at the start relay which is also in the fuse box behind the cab when I saw a black wire attached to the start circuit on the bus bar. I traced that wire to the Boom light circuit. We turned the lights on and found a small amount of voltage on the start circuit.
This was a classic example of making sure you know what exactly you are attaching a ground wire to. Just because a meter or power probe shows ground, you can't automatically assume that it's a chassis ground. This is the first FLD I've worked on, I'm undecided if the rat's nest in the center of the cab under the dash is a good thing or not.
Sorry did not see the OP until Now!
Same