Here's the best link for testing Renix sensors: http://www.lunghd.com/Tech_Articles/Engine/Basic_Sensors_Diagnostics.htm
That being said, I noticed you have had Jeeps in the past, all 91+ with HO engines. If you can, find a 91-92 MJ 'cause you won't be happy with a Renix system. I've had both, there's no comparison. The Renix system is a bastardized conglomeration of sensors cobbled together when AMC was on the ropes and going down the tubes. When one sensor goes, it can cause the same symptoms as another, and they all interact with each other. Renix electronic parts are getting hard to find, and are mostly expensive. Unlike the HO engines, it's hard to find go-fast parts for it if that's what you might want to do later.