A few years ago I was an employee for a short time for a big petroleum transportation company, and drove a CH Mack. It had a 400 and when it ran, it ran just good enough so I wasn't mad all the time. It also developed that electrical gremlin one time where I was going along and it'd literally shut off. One day it happened 12 times in an hour, I was loaded with 8500 gallons of gasoline going up the NY Thruway from Albany to Saratoga to a station. I had to keep starting it back up going 65 mph to get to the station to unload. Something about electrical problems...and GAS...I'm not sure what it is, but it was making me a little nervous.
I called the so-called "mechanic" for the outfit, and for the first time in his life admitted he didn't know what it was, so bring it to Mack. It ended up being the wiring harness that plugs into the firewall that feeds ecm and a few other things. 4 feet of wire and labor was over $600.00.
Shortly after that I remedied the entire problem by purchasing a '97 Peterbilt and became an owner-op again even though I said I'd never do it again. Electrical problems ended, but a whole new series of problems developed at that point...like all truck owners can relate to.