Tail light grounding anomaly

[dsnyder78]

I recently did a bed swap on my truck, flare to fleet, I had zero issues with my previous taillights what so ever. Installed the new to me bed, and now my passenger side taillight is extremely dim. So after a little troubleshooting, I now have an extremely bright tail light, but the side marker light is inop, like all the power going to the housing is going to through that filament. If I pull the housing off, all bulbs will be lit, but very dim (original problem). If I make a jumper wire, or reinstall the housing, that running/brake light is super bright. Obviously have a grounding problem, just not sure where. I cleaned all contacts with wire brush (exposed terminals at least) and sprayed contact cleaner on them as well. I took the ground off where it screws in behind the housing and cleaned the surface and verified good contact. The left taillight functions 100% all the time. So i know the problem lies between the two lights in the harness.

Any insight would be appreciated.

[69Ford]

Try grounding the new bed to the frame of the truck. The new bed may have paint, rust issues preventing a good ground to the frame.

[dsnyder78]

Well, on the way home from work, I noticed the side marker light light up when I applied the brake, something is wired backwards, shouldn't be hard to figure out. I will install an grounding wire from bed to frame

[Busboy]

You definitely have a bad ground on the tail light housing.

[Nitekruizer]

You more than likely do have a ground issue. The reason that one tail light is so bright is likely because the brake light filament in the bulb is lighting up with or instead of the tail light filament. Is the wiring harness of the new bed visible? Someone may have repaired it and spliced it wrong at one time. Something else to check if the grounds all check out okay. Check the grounds first.

[dsnyder78]

New bed didn't have any harnesses, I just used the old harness to the housing on the new bed. I will see if someone extended the harness at some point and go from there. Last resort I'll make a new harness from the pigtail from the drivers side to the passenger side. I'll keep you guys updated.

[sargentrs]

Be sure and check/clean the sockets really well. I had a '74 Dodge with an intermittent taillight problem that gave me fits. Finally discovered rust in the dimples in the socket where the pins on the bulb lock in. Cleaned thoroughly with some steel wool on a screwdriver and no more problems.