Whenever I step on the brake pedal in my 85 D150 the gas garage goes up and the brake lights barely come on. I’ve yet to fine anyone having/had the same issue as me. The blinkers are also very faint and cause the gas gauge to go up. Would this be a grounding issue or just bare wires? Anything helps.

 

Likely a bad ground somewhere. Have a look and see if any of those systems share a common ground. Cleaning it, and making sure it IS a good ground, will likely fix it.