Purney,
The black box on the firewall would be the voltage regulator. I don't think there is any fuse for the fuel gauge. When you install the new cables, make sure the ground strap has a clean place to bond to. Batteries can be deceiving..make sure it has clean posts and a full charge. If it is questionable, have it load tested or buy a new one. With the fat cables you are going to install ( great sleuthing) and a charged battery, the truck should turn over briskly. Good luck and a belated welcome to the Stovebolt.
Stuart
