Voltcraft rt 100 tester voltcraft rt 100 p the voltcraft rt 100 automobile relay tester is intended for making fast and easy checks of most current automobile relays with 4 or 5 connections the tester performs a full automatic check of the relay and indicates the result with a light green ok red error br the test is performed at the coil and contact side only one relay can be tested at a time p p the automobile relay tester requires an automobile direct current of 12v to opera