I'm working on a 92 Buick w/3.8 and trying to figure out why there is no RPM. The engine has no spark, fuel injector pulse or indicated rpm on the scanner. I want to verify the crank sensor operation. On the schematic, there are two wires, each coming from a buffer transformer, a ground and a 10volt reference (in the ICM). At the plug, I have two wires at about 6 volts, one at 12ish volts an one with continuity to ground. Which wire do I need to probe for the scope? Also, would this be the 18X or the 3X sensor (and what is the difference/how did they come about calling them 3x/18x)?