I truly apologize for resurrecting such an old thread, but I have experienced the engine fire twice now, and have what i believe to be some information that hopefully someone will find useful. My Brother-In-Law owns a 2006 2500HD, and has had two engine fires. The first was on the passenger side, which melted the starter. He had just come out of his mother's home, approximately 30 minutes after arriving and found flames erupting from the passenger wheel well. The second fire also ignited at the starter after the starter remained electrically energized and running, even after the key was removed. The day after fire #2, upon starting the truck first thing in the morning, the started subsequently remained energized a third time, while the truck was running. My B-I-L shut down the engine but the starter continued to run. I opened the under hood fuse panel and removed the starter relay which was stopped the starter. We felt as though we had dodged a serious bullet, as the truck was pulling a new $60K boat. Two fires and one near fire, all originating at a starter that remained energized. Three different starters, all caught fire (#2 was a factory unit from the dealer). The small purple lead that is used to light the solenoid is what remains energized. I'm suspicious that a fault in the Body Control Module, through which this circuit passes, may be at fault. We installed a normally open momentary switch inline with the solenoid circuit. So now there's a button to push while the key is turned. -at least it won't catch fire again.... Hopefully.
anybody who would like to discuss this further - just shoot me a PM or an email. I'm happy to chat about what I've found.