JAY EMRIE wrote in a message to GEORGE WHITE:

GW> GW>> (On most systems I'm used to the alternator reaches full output
GW> GW>> at about 25% max revs). The traditional solution is to up the
GW> GW>> engine idle speed - but that only works for stick shift systems.
GW> GW>> For automatics all you can do is cut down the power use (lower
GW> GW>> heater fan speed, no extra lights) or put the battery on charge
GW> GW>> overnight...

GW> JE> RJT>Not too likely for the senior citizens that are having this
GW> JE> problem.

GW> JE> Present day alternators (last 15 yrs at least) will support most
GW> JE> everything normally used (A/C, headlights, radio, etc.) in a car
GW> JE> AT engine idle speeds.

GW>Not in my experience... As I said above, most alternators only reach
GW>full output at about 25% max revs (for most people it's about 1500
GW>rpm), however they will match the usual nighttime load at about 1000
GW>rpm. On my car (less than 10 years old) the alternator goes off
GW>regulation with the headlights on at somewhere around the 1000 rpm
GW>mark, idle is at 700 rpm... You can see the headlights dim as the
GW>alternator goes off regulation.

 JE> I have a 92 ford Crown Vic and a 92 Chevy 3/4 ton PU. Neither act
 JE> that way. My previous tow vehicle, a 79 Ford 460 Van didn't either.
 JE> The head light on all three stayed bright at normal idle.

I noticed that behavior in cars that I owned that went back to the 70s, 
but none of what we have now (88 and 90) act like that.  They probably
changed something,  though I couldn't say exactly what...

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