ALTERNATOR/BATTERY IDIOT LAMP

[CLeopold@domain.elided]

       Ever since getting my 1984 Spider new in 1984 the alternator lamp (or 
is a battery lamp---does it measure voltage or amps.?)--has glowed, usually 
only noticeable at night, and the lamp glows brighter when I use more 
accessories, such as the heater blower (in hi and low speeds, different lamp 
intensities), and really glows brightly when the a/c is on, again with 
different blower speeds, brighter light.   Interestingly, when the rear 
backup lights go on when in reverse gear, they also make the battery lamp go 
on really brightly---more so than the a/c!
       I have had my Alfa mechanic at local Alfa shop here check it several 
times, and he says that a lot of Spiders do this:  he says he has never known 
why Spiders do this.
       It also seems to me that I need a new battery every 2 years.......a 
plug-in trickle charger helps a lot--stretches it to 3 years. 
       It seems to me that I might do better if I put in a stronger 
alternator. Does anyone know what the amperage rating is on the mid-80's 
Spiders, ---and would a higher amp. alternator blow anything in my Spider?
       Finally, this is academic----why has this battery indicator light kept 
glowing all the time over these years......is it possible i got a bad 
alternator from Alfa all those years ago from the factory?---or is what my 
mechanic says true---that  all Spiders do this and he  has never been able to 
figure it out?  Why do the backup light realy get the lamp to glow?
       Perhaps the resistance of the bulb in the indicator lamp is too 
low?---it should not be this because the current across the indicator lamp is 
supposed to be the difference between the output of the alternator and the 
battery output----is it possible the alternator is fine, and Alfa Romeo wired 
the lamps incorrectly in Spiders?
       Thanks for any help from an erudite bunch of guys!  (and gals.)

-Clay Leopold
 Princeton, NJ
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