My '55 2nd series truck has the following light problem; when I pull out the light knob to parking lights everything is fine, no problems, when I continue pulling the knob out to the headlight position the tail lights go out.

The blinkers work fine, the brake lights work fine.

Anyone know what is causing this problem and how to solve it?

Bad switch

If you look for a new switch it fits 1955 & 1956 cars as well as 1955-59 trucks.Should be easy to find.

If you have had the wires diconnected off the switch it is possible that you have the rear tail lights and front clearance lights transposed on the switch connections.
Tony

Tonyw might have the answer here. It's really easy to mix those connections up. It seems that if the switch was actually bad you would have a no show on the tail lights at both positions. Someone may have tried to rewire it so that the parking lights would stay on when the headlights were on. Having failed on that attempt they may have put the wiring back to the wrong terminals.

Try pulling the switch and comparing what you have with the factory wiring diagram. It is probably an easy fix. (Famous last words)!

Thanks...it worked fine for years and all of a sudden it stopped working...

Thought maybe a wire had fallen off, but it sounds like a new switch is needed....

Thanks again, guys.