A new Turn signal switch is TW7 part # from Standard parts , you should be able to get one for around $40 , Rock Auto has them .
the extra 3 wire connector is not used in E bodies & can be cut off right at the switch.
Evans harnesses may sell you connectors or have a source , firewall plugs should be inspected also , use di-electric grease to coat the contacts to prevent corrosion in the plugs , make sure the connections are tight too .