Wierd tail light issue.

T98 4.0 auto. All lights work except tail lights. Has trailer light plug. Tore the panel open behind the spare. When I disconnect the rear ground with just a single wire i get partial lighting. The left side is about right but the right side is extremely dim. Also with ground disconnected my left rear blinker stops working in the rear and semi flashes through tail light bulb. Also with ground off the tails wont shut off with the switch. When i reconnect the ground they cut out and my left blinker works correctly. Is this a bad connection somehow back feeding? Please help.

Factory/Mopar accessory tow harness, or aftermarket? Seen MANY problems caused by aftermarket "solid state" boxes melting internally. Could be a blown bulb. I've seen the filaments touching the wrong posts and back feeding.

Is the trailer wiring adapter plug and play, or cut n splice ?

Take your $6-15 volts/ohms multi-meter that you purchased at your local hardware store, home improvement store, or WalMart type store. Test for 12 volts at the bulb sockets. Test for continuity to ground at the bulb sockets. Re-test for both at the wire plugs behind the spare tire. Test the 3rd brake light.

Unplug and remove the trailer wire adapter and test again. Test/inspect for wire continuity and short circuits on any circuits that fail.

Check for corrosion in the wire plugs. If there are any relays, test them or swap them around.