bad grounds do weird things as a load will try to pull from the least resistance, and when that's note straight to ground, and can pull thru all kinds of other stuff.
you'll see it with trailer wiring a lot, bad ground and you'll hit the brakes and lights on the dash can some on like wtf.
both battery cables and check if you can find the ground strap. I don't remember exactly where they are on these trucks. usually back of the block to firewall or side of the block to frame somewhere. clean them all, Dielectric grease and tighten.
you'll see it with trailer wiring a lot, bad ground and you'll hit the brakes and lights on the dash can some on like wtf.
both battery cables and check if you can find the ground strap. I don't remember exactly where they are on these trucks. usually back of the block to firewall or side of the block to frame somewhere. clean them all, Dielectric grease and tighten.