<Quick test:
<Disconnect the field wire to the alternator. With engine running (idle
<or a little above ...
< ... temporarily connect a
<wire from the battery(fuse box etc??) to the field terminal ...
<John Series IV(ish)
Sorry John .... bass ackwards for the stock alternator.
The following applies to the STOCK 10AC Lucas alternator system.
The 10AC is an antique design and differs from most modern
configurations and therefore tests a bit differently.
A proper test procedure to isolate the fault...
1 pull the "Lucar" terminal off the F lug of the regulator.
2 Turn ignition on but don't start the engine.
3 Measure the voltage between the lucar (female) terminal and
ground. It should be close to the battery voltage.
If no voltage is measured the Alternator field is open, the
6RA control relay is dead or the wiring between them is broken...
Follow the circuit back from the F terminal to the Alternator
field negative contact (mostly exposed) , through the 3.5 ohm
field resistance and back to the field relay then to the
battery.
My bet is the brushes in the alternator are worn giving an open
field... they are easy to replace.
4 If Voltage is measured .. Start the engine.. If the voltage
drops or jumps around the brushes / sliprings are worn or dirty.
Clean and replace as necessary.
5 If all of the above seems in good order connect the Lucar
terminal to ground. The engine should load a bit and the battery
voltage should increase. Do not allow the battery voltage to
exceed 15 Volts. Disconnect the ground if it approaches 15 V.
An ammeter should show charging. If this happens the alternator
is good, and the 4TR regulator or it wiring is the likely
culprit. Check to see the regulator (-) connection is well
grounded, by using it to ground the F Lucar terminal.
If you measure more than a volt from the 4TR (-) terminal to the
engine block, with the ignition on and everything connected the
ground is defective. Check for corrosion.
If the lead to the (+) terminal of the regulator is broken you will get
overcharging.. something you are not complaining about....
In doing all these tests and almost anything else with the electrics
a good voltmeter - ohmmeter is a real advantage. Of late excellent
quality pocket sized digital meters have become very affordable.
My personal favorite is the Fluke 77 series.
Steve F
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Steve Finberg W1GSL w1gsl(at)mit.edu
PO Box 397082 MIT Br Cambridge MA 02139-7082 617 258 3754
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