Have you noticed, like I did, that the factory Bosch alternators doesn't seem to put out much voltage? I was curious about this and had a chat with my local rebuilder. What I learned was the Bosch voltage regulator caps the maximum alternator voltage at about 13.5 - 13.8 volts and tends to drop as the alternator gets hot.
The solution I found is an Adjustable Voltage Regulator. This regulator will allow a maximum voltage output of 14.4 volts. For comparison, this is the voltage that you will find on most if not all domestic vehicles. With the Adjustable Voltage Regulator installed on my 1993 968, the results were brighter lights, no drop in interior fan speed when the second cooling fan kicked in, tighter bass from the aftermarket stereo, etc. Basically solved all the issues associated with alternator low voltage were completely eliminated. I now find the dash volt meter will stay right on the 14 volt mark with the stereo, lights, A/C and wipers on (Basically everything possible turned on). A tremendous difference.
The Adjustable Voltage Regulator replaces Porsche part #928 603 142 00 and will fit:
911(C2/4 & 993) 89 - 98
928 87 - 95
924/944/968 83 - 95
It is a direct bolt-in replacement. A couple of screws and a wire to remove and plug-in replacement. Easy!
The Adjustable Voltage Regulator retails for $45.95 plus $5 shipping. You can get additional information and how to order by going to www.prospeedmktggrp.com . For the regulator (and info on high output alternators) click on the "Electrical" button. For ordering information, click on the "How to Order" button or call, toll free, 866.968.944
Michael G. Wachholz
400 Pond Ridge Circle
Wayzata, Minnesota 55391
866.968.2944 toll free