93 obs ls swap engine keeps running after key is switched off

I’m helping a friend with an ls swap in a 93 truck. The engine will fire up and run fairly well but when you switch the key off the engine keeps running. We have put a new ignition switch on the column, in hooked the alternator to eliminate back feed as a possible issue. The ignition fuse has no power with the key off but after the engine is running and the key is switched off the ignition fuse will still have power. We have also checked and traced wires but we have not found any issues with that. We are at a loss anyone else had issues like this? At this point we are open to try about anything