smelly catalytic converter?

Don't just go after the voltage regulator , I'm glad you found the source but now you gotta find the cause. Since you've got a Cummins , your alternator is more than likely a leece- Neville or delco. Both simple. 2 wire alternators . Hot cable n ground. I'd have both batteries checked. It only takes one shorted cell to screw everything up. Those alternators can be pretty pricey. Good luck.