Your O2 should be fluctuating, not steady. If it's steady, you have a
problem and need to find it. Could be the sensor, an exhaust leak, the
wiring, or some other problem entirely.
My presumption is that the water temp sensor is bimetal, but I've never
attempted to look at one. It is supposed to change resistance depending
It will be very difficult to check individual items with a voltmeter,
especially in the fashion you suggest. Ideally, you'd hook up a scan tool
(which I'm sure you don't have) and look at the readings and flag anything
which looks suspicious.
One of the difficulties here is that it's difficult to know where to send
you. On the one hand, an O2 fault code almost always points to a faulty
O2 or leaking exhaust, but on the other hand, your case suggests some
issues with the wiring. So I'm reluctant to send you into a painstaking
inspection of the components with a voltmeter.
Not seeing the wiring repair work, it's difficult for me to know how the
repairs were made and how well they were sealed. This can have a great
deal to do with how water intrusion would affect the circuits in question.
I guess you need to decide how sure you are that the wiring repairs are in
good condition and correct, and let that be your guide as to whether you
should start investigating elsewhere.
Hope this helps.