Alternators can not charge at 10, 10.2, 10.7, 9, etc. Volts....
First, When a voltage regulator fails the battery light or gauge will come on indicating a charging issue. Continued driving will discharge the battery and is not good for overall battery life and condition. If you tested the system showing a reading of 10.7 Volts (or other reading lower than 12) then the testing is not done with a fully charged battery and not going to be an accurate charge system test.
Even without an alternator installed on a vehicle running voltage will be 12 until battery is drained. An alternator will not show a reading of 10.7V. That reading is only whatever battery state is. Battery condition will effect charge rate. Bad or discharged battery will not accurately show what cause the voltage or charge issue.
Battery Condition Matters - Its the whole charging systems buffer..
If there was any other battery drain condition and you went to check the charging system with a drained battery (11.8V is 0% state-of-charge), then even a fully capable alternator will show low voltage. The reading would be very low as the weak battery buffered down the voltage by the extreme load of the battery in its discharged condition.
...BUT Anything is possible... The alternator can still be bad. A bad test procedure doesn't mean the guessed diagnostic is wrong...
The first information I hear from anyone having any difficulty with their charging system is how everything has been checked. Everything. All else on the vehicle is working perfect. Checked by state of the art equipment with a master certified trained faultless technician with 30+ years experience.
Countless times this is not the case. There are times a well trained master certified technician has cost his customer extra time and possibly extra $$ on unnecessary repairs. Hopefully not yours.
Is it possible that after discovering a broken field wire the misdiagnosed alternator failure was brought to the car owners attention with an apology?
At the mechanics expense, the alternator that already has been sold and installed is then removed and the original good alternator is then re-installed adding 2 additional hours of labor time for the technician??
No charge to his customer for all this, right???
The new cost to the customer is the $45 to repair a wire instead of the $380 already sold and labor performed!
I guess it is possible. I have never sold an alternator to a technician who asked for the good old one back after originally mis-diagnosing so that he can re-install. That is extra time and labor and headache.
There is a chance that the mechanic will pay out of his pocket the alternator... He will decide to admit the error and not get paid for all labor performed. Again, anything is possible.
There is also chance that the car owner gets a call saying, 'After we installed the new alternator, we were able to do some further checking and found a plug needing replaced. It maybe caused the ORIGINAL ALTERNATOR FAILURE. It is only an additional $45 to replace and ensure the proper function and life of your new alternator'.
You are now emotionally driven to this EXTRA repair that must be done because it might cause you the same issues.
Some of you are now wondering about those multiple call backs from your trusty repair shop... Was it an original mis-diagnosis? How many things have you paid for and not really needed?
Back to your charging system inspection...
We will not argue. We will only provide information. We are also trained; have master certified technicians and Industry experts within a large association backing up the information we provide. If the battery was in a discharged state (doesn't mean it is bad) it can not give an accurate charging system check. No matter what.
You must start with a good, fully charged battery to perform a good accurate test. I have told countless trained technicians this same thing after asking how to get the new alternator to charge after they installed. Unfortunately official looking certificate pieces of paper sometimes do not mean much. Ask any real technician and they will agree with that. They also agree there is always more to learn no matter how many pieces of official paper they have garnered.
I am glad in your confidence in the mechanics/ technicians you have. Good mechanics and technicians for the automotive industry know and understand there are fewer real professionals with this profession than anyone truly can imagine. It is an unfortunate circumstance that hurts the entire profession. If you want to start explaining that your master certified experienced technician checked your alternator and its only putting out 10.3 Volts, this voids out your technician.