The advice was......
Simple: With a reasonably accurate voltmeter (almost any digital one),
measure the output voltage with the engine running. You should get at
least 13.5 volts. For the most definitive answer, check
the voltage between the two actual battery terminals (NOT the clamps!).
Also check with the lights on and off, and at idle
and higher RPMs. You can also use the voltmeter to
check for excessive voltage drops in the wiring and grounding
(e.g. check the voltage drop between the negative battery terminal and
the car's body. More than 0.2 or so is fishy.) No need to
disconnect anything to do this these tests.
Note that a old, almost worn-out battery can mimic the
symptoms of a bad alternator: The car normally starts OK,
but if you leave the lights on for 10 minutes, it will no
longer start.
Doug Braun
'72 Spit
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I didn't have enough Amps to crank the starter so I boosted the car. I
took the voltage measurement on the battery posts and got 12.0A at idle.
Increasing the engine revs had no effect on voltage at the terminals.
Turning on the headlights dropped the voltage immediately to 11.3A. It
continued to drop to 8.5A before I switched the lights off. Given your
advice and my results I'm thinking that the alternator is kaput.
Is there a domestic replacement alternator that I can try that is a simple
bolt on, or should I just source the Lucas?
Alan
78 Spitfire
Mississauga, Ontario
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