1-Wire Timing LightChecking the spark in relation to the piston ensures that your engine is firing as efficiently as possible. The Tac Style Shift Light from PROFORM allows you to check timing, help diagnose a no spark condition and check for electronic advance retard! Use with 2, 4, 6 and 8 cylinder applications. Featuring 1 wire inductive lead design and a high intensity LED that's visible in sunny conditions, which makes using this tool simple and easy to use.