2000 Peterbilt engine won't shut off

Recently my husband's 2000 Peterbilt was vandalized and all four batteries were stolen and they attempted to cut thru some copper wire. Long story short, he replaced the batteries and wiring, but now the engine won't shut off unless he disconnects the battery(ies). He checked with our local Peterbilt shop thinking he needed to have the computer reset, but they
had never done it. Now he is attempting to install a toggle switch so he
can shut the engine off more easily.

I am sure I probably lost something in the translation here between my husband and I, so if you need more details, let me know.

Any suggestions?