Classic/Antique Car Repair: 1964 ford f150, double filament, filament bulb

Question
QUESTION: Why do the tail lights go out when the head lights are turned on?

ANSWER: When are the tail lights on? has the truck been restored or rewired?
Let me know.
Brad

---------- FOLLOW-UP ----------

QUESTION: The tail lights work when the brakes are applied.  The truck has not been restored or rewired.  Thanks, Ken

Answer
Ok, here is what is happening. The rear tail light bulbs are double filament bulb, one for the tail lights, which are not as bright as the stop lights, and the other for the stop lights. The tail lights are used more than the stop lights and it is possable that the tail light filament is burned out on the bulbs. So I would first check the bulbs to be sure that they are ok. If the bulbs are ok then I would take my handi dandi test light and probe the socket with the headlghts turned on. If there is no voltage to the sockets then I would check the fuse on the back of the headlight switch. If it is ok and still no tail lights let me know and we will go to the next steps.
Brad