Holding Tank Wiring - Test wires

I would suggest to check the white wire for continuity to ground. You could then measure resistance from the other individual wires to the ground wire. While you're about that, you may wish to power a turn signal and see if there is voltage on any of the colored wires. It is almost too much of a coincidence that the mfg would use a trailer harness standard for tank wiring.

I do not think they are "test" wires. Sounds like the normal connections from the wiring harness to the sensors on the tank. Someone was sloppy allowing them to hang below the bottom of the trailer. Chino

These wires are definitely connected directly to the sensors or sensor wiring on the tanks, not running lights, although the colors might make one think of running lights. When I had my tanks exposed a couple of years ago, I noted that the wires were attached to the tank sensors but did not document exactly what was attached where. I have seen some material saying that different levels in the tanks will produce different resistance in the sending wires. The question is how to use these wires to do that testing? I know this forum has some pretty adept people when it comes to electricity and likely they have the correct answer.

I'm also wondering if trailer manufacturers other than Northwood/Arctic Fox provides these wires so that troubleshooting might be made easier (if only one knew what to do with them)??

Those are the standard colors for the running, brake, and turn signals. They could be tank monitor wires but I'd connect it to a vehicle and check to see if they were powered when the different lights are on.

I guess that would be coroplast. Chloroplast is part of a plant.