voltage regulator

[robert weinberg]

the volt meter on my car has usually been around 12.75 volts with the lights off 
- but with the lights on, we are talking about less than 12.5 - then when the 
aux fan kicks in while the lights are on, it sometimes dips for a split second 
below 12 volts. the headlights dim and the engine rpms drop below idle.

i'm assuming this isn't normal ;-)

question is this usually a symptom of a worn voltage regulator? or the 
alternator - i hope it's just the regulator.

if so, which one is for my car - the 28mm or the 32mm? and has anyone tried 
these units? my friend has one on his 4000q and says they work great - 
especially because they are adjustable:


This is the 32mm one

http://cgi.ebay.com/ebaymotors/Voltage-Regulator-Bosch-Alternator-Audi-Mercedes-VW-_W0QQcmdZViewItemQQhashZitem35ae444e15QQitemZ230556978709QQptZMotorsQ5fCarQ5fTruckQ5fPartsQ5fAcce


This is the 28mm one

http://cgi.ebay.com/ebaymotors/Voltage-Regulator-Bosch-Audi-Porsche-Mercedes-VW-73-93-_W0QQcmdZViewItemQQhashZitem4cf37898a4QQitemZ330502281380QQptZMotorsQ5fCarQ5fTruckQ5f