I had the chance to use this at a shop this week when trying to track down my friends 2jz swapped mk3 wiring harness problem that was preventing the car from running. This tool ended up being a god sent and really helped me track down the problem. I highly recommend it for anyone doing wiring on their car! I plan to pick one up in the future so I thought id pass the tip along. Watch the video:

http://www.powerprobe.com/powerprobe/Home.html