behind the cluster to the left is a 6mm bolt,,(10mm wrench) clean them, scrape off the heat shrink glue from the eyelts and throw the start washers away.. same approach at the fuse panel, right side in the cab,, then...... clean the big ground bolt on the engine block in front of the starter,,, (15/16" wrench) if it is loose,, you found the issue.. there is ground cable from that bolt to the frame straight off of it behind the steer tire.. clean the frame ground.. (15 mm wrench). on the firewall next to the starter relay is a black ground breaker..(13mm wrench) clean the ends,check for dry rot and cracks.. then the starter grounds..(3/4" wrench) I assume you checked the battery cabels.. If there is a fused link on the batts,, check it out.. (9/16" wrench) .. Keep in touch... Jojo