steves66c20,
Don't give up. The taillights and brake lights come from different sources, so whatever the problem is must be in the lamp assemblies or a ground issue.
The 'ice pick' style voltage tester allows you to ground the pigtail and probe tight little places, like the contacts inside a light socket.
On your rig all these circuits are fused, so a dead short would result in a blown fuse. If all the light functions are dead on BOTH sides, the commonality to this scenario would be a lack of a good ground. Keep poking around and keep us posted.
Is there a plug setup on the firewall that involves these wires headed back toward the rear of the truck?
Stuart
