Check the listing for details. in-line spark plug ignition tester. Condition: Used. Listed at 10.00 USD. The in-line spark plug ignition tester is a diagnostic tool designed to check the ignition system of a vehicle. With the manufacturer part number ttgt4, this spark plug tester allows for easy and convenient testing of the spark plugs to ensure proper functionality. Perfect for automotive enthusiasts and mechanics looking to troubleshoot ignition issues, this tool provides a quick and reliable method for testing the spark plugs in a vehicle.