Power probe is a must for diagnosing electrical. One of the best tools I ever bought. I bought the first or 2nd version back in early 2000’s and that thing has saved me so much time it’s ridiculous. Its my go to tool. I rarely even bother touching a old trst light anymore. A lot of people dont get it but imagine having the ability to instantly test for power, ground, continuity, AND apply power, or ground, or BOTH at the same time to test a electric motor or relay ALL WITHOUT EVER HAVING TO JUMP POWER OR GROUND with jumpers. The newer ones even show voltage.