Trailer Lighting Issue

Long time lurker, first time poster.

I’ve got an issue with the LED trailer lights on my 1987 that I can’t seem to diagnose. I spent a good long while yesterday troubleshooting and think I know generally where the problem is but not what the problem is.

Good news: the trailer lights work at the trailer. I hooked them up to the flat four of another car and all is well.

Okay news: they kind of work when connected to my 1st Gen. They light up ever so faintly when I press the brake and flash correctly when I use the turn signal.

I’ve got the Hoppy converter that plugs directly into the rear light harnesses. All of the lights on the car side work except that the left blinker is a bit fast now.

With the multimeter I’m getting 12v through all three connections at the converter before it connects to the flat four plug. At the end of the flat four plug that goes to the trailer, I’m only getting half a volt at rest and 2-3 volts when the brakes are pressed. I ran a connectivity test and I get between .1 and .4 ohms on the brown green and yellow wires. I also get the same reading between the negative post and the spot where it’s grounded into the frame (touching both the end of the ground wire and also touching the frame. It’s grounded at the very end of the bed below that plastic piece that covers the back of the carpet before the tailgate closes. It’s touching bare metal and screwed right.

what could be causing the low voltage at the very end of the plug? I was thinking a bad ground but the connectivity test seems to suggest that it’s got a clean connection to the grounding point. should I be grounding it to something else?

 

Welcome to the forum.

Is this connection free of corrosion that you can see, based off of the voltage drop you are seeing?

 

As far as I can tell the connection at the plug are clean. The connection between the plug and converter is spotless and the plug going to the trailer is a little dingy but not corroded.

I re-did the ground yesterday so that’s spotless.

 

Are the wires going to the plug to the trailer connected with those disgusting "vampire" clips? If so, did you try wiggling/jiggling where they're clamped on, while checking the voltage for changes? They're notorious for bad connections.

Just a thought...
Pat☺

 

Blinkers have the old style warning signal, fast blink means a bulb is out. Since LED's draw so little current, the system thinks a bulb is out when an LED bulb is used.