International 4400 Tail Light issue

Hi there,
I own a 2005 International 4400 truck that is set up as a hooklift dumpster truck.
I ran into an issue initially with my parking lights. During a rain storm, I turned on my headlights from
inside the cabin rather than just using the daytime running lights. While sitting in neutral, air brake, I turned the headlight switch on and my backup alarm started charming even though I wasn't in reverse. Shut headlight switch off and backup alarm shuts off. That short or whatever happened, caused my parking lights to go out and they've never come back on. All fuses and modules are good.
I went to the wiring control junction box located towards the back of the truck where the wires from the cab of the truck are run and split before reaching the tail light area. All connections there are good, dry, and clean. At the back of the truck, under the bumper is there the wires meet and branch off to the blinkers, reverse lights, parking lights, etc. Most of the connections / ends were corroded to I cut and replaced them one at a time without messing up where they were screwed in. I also cleaned corrosion from the plugs at the back of the tail lights and reverse lights. Now, I have power all the way to the tail lights but
apparently not enough to make the lights visible from the outside. I can barely make out my hazard lights then hazards are on. I literally can barely see the lights blinking. Any idea whats going on?
Thank you,
Pat