old54truckluvr,

Lots of stuff going on...here are a few thoughts that might narrow the troubleshoot down a tad. The brake light filaments are the brighter of the two in a dual filament bulb. A flashing turn light is the brake that is flashing. Headlights on or off should not have any effect on turn signal operation...remember, the turn signals are brake lights that flash and aren't switched on or off by anything in the cab.

A typical wiring arrangement would be three wires down the frame to the rear of the truck. One wire would be connected to both taillights, and the remaining two would be attached to a left brake/turn and a right brake turn.

If you have a multi-meter, your test for ground must show continuity between the brass lamp holder in each light housing and a ground on the bed or frame that is common with the battery.

Take it one step at a time. Try to get two brake lights of equal brightness on both side when you mash the brakes. Try to get two taillights of equal brightness when the head lights are turned on. These must be the smaller filament. Clean both sockets and make sure the contacts on the bulbs are shiny and that they are inserted in the holder properly. If you take it a bite at a time, it is easier. Good luck.

Stuart