2000 Dodge Durango Trailer 4 pin connector

My dodge has factory installed tow package, and 4 pin light connector. I have both a boat trailer and utility trailer, and in both the right rear brake/turn signal does not come on.

I used a voltmeter at the receptacle (green wire) and I'm only getting 5.5 to 6 volts. The other 2 (yellow/brown - running lights and left brake/blinker) show 12 volts. I also snipped the green wire and connected it directly to my voltmeter, thinking the brass connector was corroded, but I still get 5.5 to 6 volts directly from the wire.

I traced the wires back to the left wheel well, and from that point they are hidden. Wire looks good up to that point, no nicks or cuts.

Any ideas, please?