When I turn the key the dashboard lights up but the truck will not start.

Yes, I have looked under the truck. When the truck does start, if I wriggle some wires on the battery it sometimes starts. The battery terminals are tight. My friend and I think it is some type of grounding problem but not sure.

Tight , doesn't necessarily mean 'good' , corrosion can be between the contact points where you can't see it. Sounds like the 'wiggle' routine might lead somewhere , I'd re-check all connections associated with the harness area you are wiggling. Finding the starter may be easier said than done , but if you follow the positive battery lead that does NOT go to the fuse box , it will lead you to the starter.