Back in 1989, General Technologies unveiled a new, computer safe, all solid state electronics circuit tester . Unlike regular test lights, this high-impedance circuit tester is safe to use around automotive computers, electronics, ecm’s, sensors and air bags. It requires no wire or clip connector to ground. Rugged, built to last and simple to use on automobiles, trucks, trailers, RV’s, motorcycles, boats and any DC powered circuit from 3 to 28 volts. The tester allows users to run a test in less time that it takes to set-up a regular test light on a suitable ground.
I use it all the time in fixing electricals on my bike (s)...where I find it particularly useful is in detecting a hot wire...and the fact that I don't need a ground wire. Basically, it functions like a test light but grounds through your body...that's why you don't need to have a ground wire...so let's say you are hooking a up a radio or an extra light on the bike...all you have to do is touch a piece of metal on the bike (This becomes your ground) and test the wires or connectors with the probes...if there is juice in that wire, the tester will beep and the LED will flash... if there's no current/voltage in that wire...it simply won't do anything...it speeds things up in diagnostic work.
This circuit tester is still as popular today as it was back then...and can be picked up at any auto parts store...Check full details here