Sorry for dragging this thread up. Have a 2 wire sensor in hand and getting ready to replace.

Do you know if there is already a ground in the harness side of an 84, or will I need to check and add?

Was plug and play on my '84. The harness is set up for the 2-wire sensor so the ground is already there.

Great, thanks!

I know this is an ancient thread but it was quite useful when replacing a sensor in an '88. A few more tips for the future:

Use the method described on the first page to remove the stubborn upper grommet. A small hex L wrench goes through the center grommet hole easily and then with some medium vise grips popped out on the first try. Just watch your hands in the tight space and try to rotate it away from the other 2 cables. Speaking of which - removing the short hose that goes between heater box and the valve (2 clamps) gives you the much needed room to maneuver around too.

As a bonus if you can reach in there with a can of silicone grease it will soften things up dramatically. Use silicone grease on the new grommet as well. The new one was a bit solid and wouldn't go in but a little grease spray around the edges made it pop in there easily using just a little finger force. Same technique works with the lower grommet as well.

I ended up making a special 14mm socket out which took me a while a Dremel. That's because even though I was able to thread the sensor in it wouldn't move much past the initial screw in point even with pliers and I didn't want to damage it. It was well worth it because with that tool it was easy peasy to screw it in in no time. Alternatively if you're in the Bay Area and want to borrow the tool I have it available. :)

Overall, a bit of a pain but if you follow the aforementioned tips not that bad at all!