Alfa Romeo Repair: 1987 Spider electrical issue, light flickers, belt tension

Question
Stephen:
My 1987 Spider's electrical system cannot seem to handle much of a load. Engaging any accessories is enough to bury the Alt gauge. Alt. has been replaced, belt tension is good, ground strap is clean and tight. Battery does not loose charge, even when parked for an extended period. Electrical is so weak that the A/C fan hardly changes speeds between settings. At night the charge light flickers on and off just from the headlights being on. Also, the speedometer reads about 60% too slow, but the odometer keeps the correct mileage.
Thanks for your help.

Answer
First the grounds become corroded and resist the flow of electricity and then the positive connector plugs overheat and lose tension on the connection.

Go through and loosen clean and tighten all the grounds.
also, add a 10awg ground wire from the body of the alternator to the  engine block. Is the ground wire from engine to body in good condition...

If that does not completely cure the problem then start checking the positive connections, especially the plugs.