Hi, Art. Yes, I was hastily referring to a 240 schematic without wire colors and managed to forget that the heater circuit is two white wires with a shielded black signal wire rather than a single white wire and two blacks -at least I did correctly note that in a recent discussion we had here on O2 sensors. That's right up there with remembering that the black wire on most of the 240 in-tank pre-pumps is hot, not ground -made that mistake only once on a car running the pump backwards, won't likely ever forget that now.

I have not felt the need to go to a 4-wire O2 sensor, but I certainly wouldn't hesitate to use one. Between rusty exhaust connections and people using anti-seize, I've always thought a separate ground was a much better idea.
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Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now