I have a 1987 Dodge D-150 pickup.The right rear Turn signal or stoplight will not work.HELP!!!!! David T

If it is not the bulbs, check the wiring harness. You may have a broken wire somewhere, old mopars are known for their crummy electrical systems.

check the taillamp socket . theyhave been to get alot of corrosion in them ,

With a test light check for power, if none find the broken wire.
If you have power make sure you have a good ground. With power and ground the bulb will light.
Your old wiring system is no worse than any of the others. In fact it is better than the old jap wiring.

on the older trucks the socket that the bulb goes in would get real corroded and cause them not to work,try checking for power at the socket,if you have power their it may be a bad socket,any parts store should have a replacement in stock to fit it,good luck with it.