yep kevin, i've seen the same things
if you've ever seen the inside of these relay/fuse box's they are constructed in such a way that there are metal bars sandwiched between insulators internally. I've seen these bars break and rub through the insulators and short out causing a miriad of problems before. The only explanation we could figure out is vibration caused it.
I had a tech at the local cocacola plant show me this after they had went round and round with a couple of thier lifts until they figured it out.
Apparently moving the relays or fuses will let it work again for a short period of time. Its not a frequently common problem but i've seen it more than i'd like to. The most common issues i've seen tho is just faulty relays or bad connections at various places in the harness or on the truck where connections terminate on the frame or at a connector.

and edward is also right, if its an LPS truck then that disconnect box has been known to cause some strange issues, the most common one i've seen is not charging though, not many random codes per say, just the charging issue.