General Motors IAC Signal Test Lights For checking the electronic control module signal that provides direction to the idle air control motor on General Motors vehicles with throttle body or port fuel injection systems. No. 3051 – Set consists of Nos. 3052S and 3053S. Wt., 2 oz. No. 3052S – Signal test light for 1982 and newer GM TBI and PFI fuel injection systems with square 4-pin connector. Wt., 2 oz. No. 3053S – Signal test light for 1987 and newer GM Model 700 TBI and PFI fuel injection systems with a flat 4-pin connector.