My wife's 1993 Volvo 240 has an 'apparent' alternator issue. We have done troubleshooting as follows:
(1) Car battery was drained and would not hold a charge. Replaced with new battery.
(2) Checked voltage at battery terminals, 12.51v but was not charging when car started up. Voltage remained the same.
(3) Replaced Voltage regulator on alternator. Still no change. Battery was not charging with engine running.
(4) Checked + and - battery cables for poor contact due to corrosion. Cables were both fine.
(5) Checked alternator belts for tightness. Both within spec.
(6) Checked negative cable as follows with Multimeter: Hooked positive lead to battery + and negative lead to alternator casing... Rev'd engine to ~1500rpm, Showed a -1.59 V reading which really should not be greater than -0.05V. Can anyone tell me what may be wrong? What is best way to correct this issue? I think the Alternator is fine...

Any advise will be greatly appreciated.

Many thanks.

OnlyVolvo

You make perfect sense until you get to #6.


"(6) Checked negative cable as follows with Multimeter: Hooked positive lead to battery + and negative lead to alternator casing... Rev'd engine to ~1500rpm, Showed a -1.59 V reading which really should not be greater than -0.05V. Can anyone tell me what may be wrong? What is best way to correct this issue? I think the Alternator is fine..."


Measuring between battery + and alternator housing, you should see battery voltage, not zero. I think you just made a typo, and you mean something else?

If you meant from battery minus, then you need to check the ground wire for the alternator, between the alternator and the bracket mount.
--
Art Benstein near Baltimore

Evening news is where they begin with ‘Good evening’, and then proceed to tell you why it isn’t.

The alternator should be checked.
You could check at the b, being careful., or take it off and bring to most any car parts retailer, virtually all can check an alternator.
If it is OK, then look at the wiring. especially that at the back of the alternator.