Charging system not working
 

The charging system does not work in my boxster 2.7 2001. The voltage is lower when the motor is running. When running the voltage is 12.4 and when the motor is turned off it is 12.6 volts.

Do any of you have any idea how to fix this problem? Do i need to replace the whole alternator?

Most likely, it is the voltage regulator inside the alternator. While Porsche does not sell the regulator separately, just about everyone else does (it is common to VW, Ford, MB and other makes), so you can get one at a reasonable price.

I paid $45 for a bosch regulator about three years ago. Easy fix.