Upon trying the part store sensors (NTK and Bosch), I connected my MT2500 and they both showed a constant 4.98v output. The current sensor I have now, which is an Autolit sensor, the voltage bounces from 0.14v - 0.16v
The Autolite sensor that I have now, because the part stores sensors drained my battery, I bought on ebay because it looked like my original sensor. (ceramic with black boot on end and holes in the end that went into the exhaust). That sensor is new, it was just an older part from either a parts store or a repair shop that went out of business. And looks like it is in perfect condition.
The ebay listing showed it to be Autolite 02024 Oxygen O2 Sensor For 1987-1990 Jeep Cherokee, wrangler, Comanche. The only difference was that the connector on the autolite was a (male), connector. Wires were Grey, black and yellow. Where as my original sensor had female connector with grey, black red wires.
Looking at the 87-90 cherokee FSM, it showed that the Autolite ebay sensor was for the 2.5 liter with the yellow wire going to ignition and the grey wire going to ECU and black to ground.
Where as the FSM showed my original 4.0 sensor as having the grey to ECU, red to relay and black to ground.
Because the ebay autolite had a male plug, I replaced the it with the female plug from my original sensor. Grey to grey, black to black and red to yellow. ( I soldered the connections).
Is it possible that the o2 sensor for the 2.5 liter behaves differently than the 4.0 liter sensor?