The door ajar alarm keeps going off in my truck , anyone know how to slove this problem ?

Check the door switch. It may need replacing or the door surface may be somewhat dished in, preventing the switch from shutting off.

I take it the dome light comes on with it, Open each door 1 by 1 and push in door switch, may help locate bad one, then see if dished in, may be able to adjust or build out. Seen it happen once, but it does happen.