Sounds to me like a grounding issue. Might check the ground points under the hood, by your feet, and in the back by the tail lights.
I had light and mainly dash issues on mine. I ended up running separate grounds from all those points all the way back to the battery.


Got torque?
'02 Ford F-350 STD Cab V10 6sp 4x4
12MPG in town and 15-17 on the highway.