What would cause my car to die once I release the ignition switch on 1991 Mercury Capri

My car starts but dies immediately once I release the ignition switch

Asked by for the 1991 Mercury Capri
The ignition switch is bad.
Most likely is switch , but is fuel pump cicruit also a possibility? comes on for 2 sec 'crank' then relay releases in run position?Or other related part of control system. ALL can be tested , but yes if we only have a choice of one part for now , Id go with the switch...............never mind.