Starter finally went up in smoke (literally) on the ole' battletruck.   2000 Silverado with 160k miles.

Ordered a new AC Delco replacement.   I did the standard bench test in my vice with a jump pack and jumper wires.   Tested all three terminals.   Passed.  

Go to install it on my truck,  as I reconnect the battery - the fucker engages.   No key in the ignition.

First guess was a bad starter relay or ignition switch,  so I disconnected the ignition wire from the terminal on the starter.   Only thing connected at this point is B+.   Sure enough,  starter fires up again on its own.  I remove the starter,  bench test it,  and it does fine.   Now,  Im baffled.  

Ignition wire and B+ test fine at the starter with the multimeter.  

Is my starter/truck haunted? How the hell is the starter motor engaging and spinning with only the B+ wire attached?   And why wont it replicate this behavior during bench test?  I even double checked the B+ connection at the starter terminal to make sure it wasnt shorting against the case or contacting the other ignition terminal.   No issues.

Good point.   Might explain why the previous went up in smoke with no warning.  

Prior to that,  I was changing a bad knock sensor,  might have rubbed/bumped/pulled the wire out enough to create a short while pulling the intake manifold.

Ill trace the B+ wire back to the source and look for damage.   Thanks.

Pull the starter relay, may have the contacts burned/welded.

Also, possible to have defective ignition switch, or  screwed up remote start scab wiring.

You possibly have a ignition switch issue or the relay has failed closed. The last starter failed because of the issue, starters seldom get hot enough to catch fire unless they are engaged so long as to oveheat the rotor varnish [insulation] coating or plastic bits.

Thats what I thought at first,  but I eliminated that as a possibility when I pulled the ignition switch wire off the starter terminal.

Gonna use some heavy gauge wire to jumper the battery to B+ on the starter.   I suspect a short in the existing harness as the first poster mentioned.

I award you a million Internets,  good sir.  

There's a protrusion on the ring terminal of the B+ cable.   It got bent and was barely contacting the ignition terminal.   Only way I was able to spot it was inspecting the cable with a pocket mirror and a flashlight.

Not much wiggle room on the 5.3 starters.    Can barely see the posts on the starter when its mounted,  much less spot something like that.