my 91 pickup has this issue since i bought it recently the previous owner was an old timer so he forgot to metion this problem. I had a night off of work with the family left around 7pm turned on the truck turned on the lights it was ok till i started on the road.everytime i hit a bump it flickers on and off sometimes stays off for a while and when i turn left and eight it does the same.im guessing im grounding off somewhere or maybe just a wire with bad connection but i dont know where to start . Any ideas ??

 

Follow the harness towards the front lights. Open up the wrap and check the wires in there. Might be shorting somehwere