I have a 1978 Ford F150 that ever sense I swapped the bed I have had issues with the rear tail lights. If the truck has been sitting for awhile and i turn the lights on the will all come on, but after about 20-30 seconds they will all shut off in the rear, cab lights and headlights stay on. if i turn the lights off and turn them back on they will come on again but for a shorter amount of time than last time, it will continue to do this until they will not come on. Any ideas on the possible issues? I am picking up new sockets and bulbs just to be sure that those are new as well.

 

Sounds like a ground issue. Cleaning or replacing the sockets should help. Next step is making sure the sockets have a clean ground to the bed and the bed a clean ground to the frame and ultimately the engine block and battery.

One check would be to get a 25' length of light wire and attach to battery negative. When the rear lights go out, contact the ground wire to a tail light socket housing... if the light comes back on it is a ground issue for sure.

The bed is usually grounded to the frame by its bolts and the frame to battery by (at least) 10 gauge or heavier wire from the battery to front radiator housing. I added another ground from engine to frame on mine for backup. Dirt or rust at ground locations can mess up the lights.

 

so would having a bad ground on one side effect the other side as well? cause both sides go out at the same time when they do

 

According to wiring diagrams, there are separated grounds. If it is a grounding issue, maybe it's the engine to cab? Maybe replace it anyway if it looks crusty, and while your looking at the grounds, add one from engine to frame.

But, the first thing I thought of when you described the issue was a tripping circuit breaker. They work by heat, and if too much current goes through, the thingie heats up and opens the circuit. Then it cools down and makes contact repeating the cycle at shorter and shorter intervals. There's a couple inside the headlight switch and sometimes the headlights will do this. The other circuit breaker in the headlight switch is for the park lights and if it's tripping then all park lights would go out.

maybe a previous owner butchered the rear lighting wire harness to add a trailer plug, so then ya gots some head scratching to do.

 

If both lights are grounded to the bed and the bed is losing ground, that could make sense...

 

check the plug @ the rear were the tail lights plug into

 

Its either a ground problem or the 4 prong factory plug on the driver side located after the rear axle in the frame.

 

Thank you guys for the info! Wiring is not my expertise, im gonna look into all of the mentioned possibilities

 

Take it one step at a time. These are simple lights, 4 wires going out back supply positive while ground supplies negative.

 

i would take the light wireing of your old bed and hook it up to the new bed, if possible that is.