2000 Tundra trailer wiring not working

The wiring for my trailer doesn't seem to be working. The truck has a separate trailer 30A fuse box and the fuse appears unbroken and good. I've confirmed it is the vehicle not the trailer and after replacing the connector (looked corroded) it still doesn't work. I tested the plug in immediately upstream of the trailer connector and no apparent power. Looking at the fuse box wiring under the hood - it has a separate fuse box just for the trailer labelled fuse 38 - more carefully and following it around it does a split. The small red and white wire splits off further into a wiring harness but the split with the thick solid white wire was not connected to anything. It looks like it should be connected to something like the engine block or the battery connector. I tried the engine block and it didn't fix the issue, still no power to the trailer. Should I connect this to the negative battery terminal? The positive terminal? Thanks.