1977 Dodge Truck starter relay

Could be the starter, starter relay, park and neutral position switch and ignition switch

Please put some punctuation in that one long sentence so it makes sense.

"nothing happens it does start but this happens sometimes"

Any other symptoms such as no headlights, no click from the starter relay, one loud clunk from the starter, etc. Do the headlights dim or go out when trying to crank the engine?

Any of the things mentioned by rasmataz could be intermittent as well as the battery cable connections. That's where watching the operation of the headlights can provide a valuable clue.

Caradiodoc

There's 5 things gonna happen with the H/light or by using the dome light when you attempt to start-Very good clue/hitting Mr. Caradiodoc keep it up and I'll request that you be selected as a moderator I'll be watching every step of the way-Don't be surprised when you get notified change of status.