When I am driving the on the road my tail lights do not work.

Check your fuses first, park lights, I think. Pull the light switch to first click and check if your front park lights are on. If no lights are on, the headlight switch is probably bad. If the fronts work, but no tail lights or dash lights, the problem is probably a wiring problem under the dash. The same wire to the rear tail lights is usually with a splice to the dash illumination lights.

Yes, it should. But, check the connections first, as the rest work correctly. There may be a short in the light unit. Check for water ingress and a loose earth lead.

First replace the tail light bulbs. The tail light and brake lights are different filaments in the same bulb. it is very possible for the tail lights to go out while brake lights still work. And somtimes the tail lights can blow out together.
If you change the bulbs and still dont work then look for other problems.

check the relays and connections at the tail lights and under the truck, has the truck ever been off road or in deep water?

There is a circuit breaker inside the headlight switch body. It gets weak over time and use. The breaker is actually mentioned in the owners manual. A new switch is about $75.00 at the local parts store. You must remove the front of the dash to change the switch. Mine would go off and then in about 30 seconds reset and the lights would come back on. I would be driving down the road with my headlights flashing as the circuit breaker opened and closed. New switch = problem fixed.

Your ot side light come on Look in fuse box, for inst- light fuse, or if You know how to determine if a fuse is burn down, look at all light fuses, Dash Instrument, etc

i have a crown victoria with brake lights no tail lights could you help me?

you could have a broken wire for your tail lights or the wiring harness for taillights is grounding out