Front parking lights / turn signal problem

[LT102]

Discovered a problem with my 1992 Dodge D150's front parking/turn signal lights. If just the parking lights are on they are nice and bright. If you then turn on the headlights the parking lights become very dim. When no lights are turned on the front turn signals work but are very dim. If the parking or headlights are turned I lose turn signals. I'm guessing it's a ground but don't know where to start checking.

[lugnuts]

Core sppt, left side between radiator and battery. Two wires on a ring terminal,secured with a 1/4" bolt. Small wire on - bat cable attaches here also. Some years had two wires right side also.