OK this isn't that serious but this is something that could leave you stranded.
This weekend I replaced the glow plug relay in my 02 7.3 Power stroke. I disconnected the battery's and went to work. After finishing this up I reconnected the battery's only to soon discover that the Injector Driver Module relay was clicking and not allowing the truck to start. A quick search on powerstroke.org suggested I check a small electrical union post that sits on top of the drivers side inner fender, a 2"x2" black box labeled "High Voltage".
I barely touched the red wire and it broke right off. This union connects the battery's to the main wiring harness and to the computer, so without it your truck will not start or run.
To fix this problem, I crimped on a 2 gage battery lug on the thicker red wire & a smaller wire connector on the 2 smaller black wires that I combined together. I then used some heat shrink on the connectors and ran a bolt and nut to connect the 2 wires together.
Its a simple fix that took me an hour to do, including running to get connectors. It also solved an intermittent loss of electrical power that my truck was suffering from and if I ever chose to, gives me an anti theft device.
Here is more info and a pic of the offending electrical post: