I have a 1985 dodge truck the right turn signal does not work when I turn the head lights on. Does anybody know what is wrong?

Check all the turn bulbs on that side of your truck. One of them probably has a filiment that has shorted onto the park lamp filiment and is in need of replacement.

Its actually simple there are probably 1 or 2 of these problems at least that I can think of. Either there's a problem with the connection, burned out wire or something simuler, or your right signale lamp is burned out in wich case you need to buy a new one and visit a machanic.

The bulb is bad or it's a bad socket for the bulb. Those are the most common problems with marker lights and turn signals.