Gary asked;
>When we got home, I noticed that the red ignition light
>no longer burned whether the key was on or off. So here is a dumb question;
>should the ignition light go out with an alternator failure? I thought it
>was the other way around, that the ignition light would burn red if the
>alternator was turning but not putting out any current. Being more or less
>ignorant regarding the more subtle features of Lucas systems, I am puzzled
>about this. Does the lamp failure indicate some problem OTHER than the
>alternator? Can this be checked somehow? Any help here would be greatly
>appreciated. Thanks.
Depending on the nature of the alternator failure, the warning bulb may
actually "see" excessively high voltages above its 14.4 Volt rating and burn
out. Last time the Lucas alternator in my Spitfire failed, it ate 3 bulbs while
I was testing it. The rectifier stack failed rather than the regulator.
Depending on which rectifiers in the "stack" fail, the bulb may experience some
abnormal voltages due to the alternating current being produced by the
alternator. A shorted diode may allow the negative 14 volt swing of the
alternator to appear for a fraction of each cycle at the field and place a total
of 28 volts across the indicator lamp. Since the higher voltage only is there
for a portion of each cycle, the bulb does not burn out quickly... the *AVERAGE*
voltage the bulb "sees" is only slightly high, but during the high peak
voltages, the filament is producing metal vapors which condense on the glass of
the bulb until enough metal boils off the filament to cause failure. If the
bulb is blackened or looks "mirrored" on the inside, the filament vaporized for
a period of time before it finally died. This is a sure sign of high voltage
Alternating Current pulses being placed on the bulb by a shorted diode in the
field section of the rectifier stack.
regards, John Pratchios
P.S. Replace the bulb, turn on the ignition; note that the light comes on.
Start the car and note if the light comes on and gets *brighter* as you raise
the RPM. If so, turn off the engine and remove the bulb until you get the
alternator repaired or replaced. It is the rectifier stack.
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