What runs to the test socket are four separate wires wrapped in a black plastic sheathing. Late nite idea-I also have a 91 300e (recently totaled) & I've popped the cap on the test socket & I can clearly identify the wires & their respective positions & insulation colors. I'm going to see if they match up with those on the 88 300ce pins 2 & 3, & if they do I'm going to use the probes directly on the ends of the appropriate wires. If they are different, Chuck is there any reason not to just see what happens trial & error since I know that if I find two wires that give the 70% duty cycle reading indicating that the O2 sensor is OK, then I've found the wires for pins #2 &3.