After literally years of fighting a low voltage problem, it is finally fixed. I converted to the 12SI (internally regulated) alternator about 7-8 years ago. My voltage was typically around 13.2 and would frequently dip into the mid 12's at idle. I replaced the alternator about 3-4 times, as well as playing with everything else possible in the charging system. The fix? Voltage regulator. Yes, these units have an internal voltage regulator that you shouldn't have to worry about. The problem is that when alternator companies rebuild these alternators, they use the cheapest components they can find (that's why the alternator only costs like $30). Of course this includes the voltage regulator. The voltage regulator that GM designed is very sophisticated, including temperature compensation, settings on how the alternator should react to sudden changes in voltage (like when you turn the AC on at idle), etc. On the other hand, the cheap (usually imported) voltage regulators that the rebuild houses use are poorly designed copies of the external regulators, pretty much an on-off switch. How to fix it? Go to your GM parts counter and ask for their D680 voltage regulator. You'll notice it costs almost as much as you probably paid for the alternator, there is a reason. Should everyone with a 12SI do this? NO. Since rebuild houses buy different brands of regulators, it's hit-or-miss and you may be fine. And some cars may run fine with 13.2 volts. You should only do this if you need to. I had to do it because I have an EFI conversion and the computer didn't like the low voltage. Frankly I never really noticed any dim lights or slow turn signals, they always worked fine, but the EFI didn't like it. I even ran electric fans and multiple electric fuel pumps. BTW for me, I got about 3/4 volt more than I ever used to, and the EFI computer was happy. Thanks to MAD electrical (http://www.madelectrical.com/) for all their help. The guy who I talked with (can't remember his name) took a bunch of extra time to explain stuff, and really went out of his way to help. It seems like he has a PhD in this stuff, and just loves to help people. Great guy! Categorize this under "you get what you pay for"... -Bob Cunningham
