Spider Voltage boost

[ALFAXTC@domain.elided]

I having a funny problem with my charging system in my 87 Spider Quad.  If I turn on the AC the system goes down to 12-12.5V and the car starts to miss.  If I load up the system (lights, radio etc.) it gets even worst.  I know the Spiders are known to have ignition computer problems when it drop under 13V and I've got a brand new (not rebuilt) alternator in there

Does anyone have any ideas on how I can boost up the voltage so even with everything on the voltage doesn't drop below 13V without burning everything?  Is there an American alternator that would fit?

Thanks
alan
88 Milano 3.0
87 Spider Quad
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