I was working on installing a portable charger in the cab of our rescue the other day. There was an existing piece of "Zip wire" power and ground comeing out from under the panel with the master battery switch that went to an old charger. Now, I should have known from the beging that this was going to be f**cked up. The "old charger" was a regular rate charger constanty charging a portable that is rarely used. Needless to say, the dope before me didn't realize even after I told him that it was "not a good thing to do".
Well, I start working on this thing and at some point, the positive lead grounded. One would think that some little 2 amp fuse would pop. OH NO! No no no, not here. Some jackass wired this directly unfused to the big ass 00 Gauge unswitched battery cable to the master switch. Well, naturally, the wire that is now on fire is is UNDER the panel for the master swicth. The zip cord insulation has melted and is now impossible to stop the short. One of my buddies was working on some medical gear in the back when I ran past him screaming and carrying a CO2. At first he thought I was kidding until he saw the smoke pouring out of the cab

Well, I managed to yank on the wires enough (burning my damn hand) to break contact long enough for my cohort to disconnect the batteries under the hood. He added to his truck check form under comments "Wiring in cab caught fire. Extinguished. Engineer Lawrence _______ Pissed." I then had the pleasant task of calling the chief and saying "Yea, Chief, the rescue is going to be out of service for a while." "Why?" "Well, there was a chemical reaction that took place when some rubber was super heated by the rapid temperature increase of some wires due to a direct phsycial contact between the..... aww :o it. The truck caught on fire, and I'm trying to fix it. I'll call you back."
OK, that is the end of my rant for the day. This is the trend I have found with many things that I work on. I find myself often wondering what the dopes before me were thinking.