Not sure where the actual meter is. I'm not very sharp on electrical jargon, but the thing is called a potenziometer, or something like that. The oil itself will not conduct electricity (that's why it is used as an insulator in transformers), but when contaminated, the dirty oil does show an electrical potential across the supply sample. This potential reading is what the ECU will use to constantly update the life left in the oil until due for a change.

Next time you're in for a service, find the smartest-looking mechanic there and ask him. The parts man should be able to look it up, too, on the exploded diagram.

Or, I could just be makin' this stuff up.