This may not be useful, but I thought I would post it anyway.
While upgrading the engine on my 1980 TA, I replaced the alternator. Initially I had planned to use the factory GM 15SI that came with the car. Unfortunately the stock alternator brackets on most Pontiac engines have the smaller bolt spacing used on 10SI and 12SI alternators. Complicating things a little I added an EFI system increasing the cars current draw. After reading Tony Candela's book " EFI Conversions" I decided something more powerful than a 10SI or 12SI alternator was needed. My research found most alternators are rated at cruising RPM, not at idle. So a 70 amp rated alternator may only provide 35 amps at idle.
This is the current draw of various devices in amps.
Courtesy lights 2.0
Parking and dash lamps 6.3
Headlights Low 14.8
Headlights Hi 16.8
Brake lights 7.7
Horn 9.2
Trunk light .9
Rear window defroster 14.8
ECU and electric fuel pump 16.0
AC/Heat blower
Low 5.8
Med 8.7
Hi 12.5
MAX 17.1
This is a possible scenario sitting at a stop light on a cold night.
Headlamps 14.8
Brake Lights 7.7
Defroster blower max 17.1
Rear defroster 14.8
ECU 16.0
Total amps 70.4
