Running light/ turn lamp and brake light short

[Hutch998]

I've got an 86' k20, with a wooden bed right now. I'm trying to wire up a set of magnetic tow lights for the bumper, however, I can only have one of the three functions. If I turn on my headlights, the blinkers don't flash, they stay steady and the right one dims. I don't think the brake light works at all, which is random because it worked like two days ago. I've traced it as far as the firewall. I'm not sure if its stock or was changed when the engine was pulled, but there is a long 4-pin connector. The terminals don't seem to short, and I have no idea how to trace behind the firewall. As far as I can see, there are no melted wires under the dash. Any advice? I'm about to give up and pay a shop to figure it out. Thanks ahead of time.

[hatzie]

 It sounds like you don't have a ground to your tails.  If you're running just the hots to the lamps they will do all kinds of strange things.  You need to ground your lamps to the frame.

There are only 4 wires from the firewall to the tails.  They are all hot wires.

A Stock 1986 with the E63 Fleetside uses one square 2x2 four position 12015024 Weatherpack Shroud at the end of the frame that mates with a 12015798 Weatherpack tower on the frame end of the tail lamp wires.  The E56 Stake and E62 Step bodies used the same connectors. 

At the frame connector the wire colors are;

• [Dark Green] RH Bright (Brake/Turn)
• [Yellow] LH Bright (Brake/Turn)
• [Light Green] Backup
• [Brown] Running/Parking

[Hutch998]

I figured that might have been the problem, and re ground the lights, one ground on each light. They are still not working properly. From what I can see, the wires run from the firewall, to the back of the truck without additional connections. I prodded the wires with a test light, right at the firewall, and they appear to be shorting somewhere in either the connection box, or the fuse box. How would I be able to check? The little junction where the lights connect to the firewall, in a 4 pin vertical pattern, seem to be clean of corrosion or any way to touch each other.

[Hutch998]

I just tried to redo all of the wires for the tail lights, and I managed to make almost everything work. The hazards don't, which isn't a problem. But with the headlights on, the right lights dont blink. That includes even the front end. Would this be caused by a ground?

[bd]

Make sure you have the correct bulbs (i.e., 1157 or 1034) correctly installed in their sockets.  Install new turn signal and hazard flashers (there are two that are interchangeable).  If the problem persists, recheck the individual front lamp grounds connecting to the radiator support and the radiator support-to-battery ground.