US88 Ignition switch - Starter stays running

No idea your electrical experience. Be careful checking the switch, say, with resistance. I prefer to do this with power, under load. If no other load, sometimes I "rig" an old stop/tail lamp or headlamp to provide a test load.

Resistance can throw you astray. Modern high impedance digital meters can sometimes show continuity when there is actually a high resistance, and any power present can lead you wrong or in some cases damage a meter

There has been threads where the column switch contacts can "float around" in the switch. Maybe it's just defective