The Stovebolt Site Forums The Shop Area The Electrical Bay why a jumper on a junction block?

I think that big gauge wire from starter is supposed to go to ammeter and branch out, but check the schematic.
You need to address the wires ASAP. You can have some bad things happen if a short occurs. Not many, if any, fuses on that truck. Previous owners/relatives could do things that cause more unsafe conditions.