My 1979 has six ground straps, I dont' know if they are factory, they look like they have been on the truck a long time. Below each headlight under the front aprons attached to the frame,behind the front wheels by the cab/door area frame to cab attachments, front of the bed to the frame behind the drivers side cab, and one on the firewall to the engine block.
oem78 i was thinking about the strap from the cab to the frame under the right side. Doesn't the box ground itself to the frame via the box mounting bolts?? I have the ground strap from the engine to the firewall and the engine will be grounded to the battery. I think all i need now is the cab to frame strap but would like to find an OEM one and know where it needs to attach to.