I've got a 2001 Isuzu Trooper that I had bought several months ago. The previous owner had lost the key and there's no local lock smith to have another one cut. So, I ordered a new ignition cylinder and keys. I removed the old cylinder and replaced it with the new. The new one however will not completely engage in the ignition housing and stay in or function. During all of this the anti theft was set off so I'm not sure if that's an issue or not. The shift I relock cable is disengaged so that's not an issue here. What do y'all think?

The new lock cylinder matches up perfectly to the orognal one