Starter "pop" (no clicking/whirring)

[Neejay]

A few months ago, my car stopped cranking (was previously having starter issues). I just bought a reman. starter used from someone (still looks decently clean) and he said it started the car perfectly.

Well, I finally got the old starter off, and when I installed this one, now it just makes a popping noise. I also have a kill switch installed, and when I tried to make the ignition regular (i.e. direct key = start) it would make the popping noise and the car would die. I would have to disconnect the neg. batt. terminal and reconnect it for everything to cut back on. When I switched the ignition thing to make it use the kill switch/button, the starter just makes a loud POP noise. No whirring or clicking.

Everything seems to be tightened up and no corrosion. One thing that did catch my eye was that the black part that houses the connection was cracked.

Starter or ignition problem?