How to clean connector under cab (driver's side)

Bought used '02 Mazda B3000 4x4 with 90,000. Haven't been able to get it to run smooth without codes for more than a couple of days. Dealer replaced upstream O2 sensor (passenger side) and we also had him replace coil pack because got check engine light before we even got perm plates and inspection.

Passed inspection then ran for awhile but has rough idle at stop lights but doesn't stall. Got another check engine light.

Replaced driver's side upstream O2 sensor. Still had check engine code. Turns out passenger side O2 sensor bad, that was supposedly replaced. Now have two new upstream O2 sensors. Also cleaned MAF sensor.

Ran good for a couple of days, now have ABS light on and running a little rough again. Now totally frustrated and wondering if I bought a never ending headache! I have read to clean connector (electrical loop?) under cab on driver's side. Can anybody tell me if this would cause all these codes and what can I use to clean it. Have some MAF cleaner specifically for MAF sensor. Can I use that? Also where in the heck is the cold level line on the coolant reservoir?

...Whar were each of the codes you received? The actual code numbers..

1131 and 1132 for the O2 sensors.
Just the ABS light on the dash. Advance said no codes but I am not convinced they could really read ABS codes with their scanners.

For the ABS light, start by cleaning all three of the ABS sensors. Make sure all three are fully seated on reinstallation.

Normally, you must have an ABS code reader to pull ABS codes but I know from experience that not all ABS fault lights are accompanied by a code. Makes ABS issues difficult to track down at times.

Essentially, the engine/transmission harness is independent of the rest of the car so I'm unsure any of the body connections would be the culprit.

With both 02 Lean and Rich faults, I'd get very suspicious of the MAF, maybe the EGR too.