I drop to about 12 volts while the engine is running, if I turn on the following:
Engine Fan
Headlights
Foglights
Blower Motor(on fastest setting)

1. Is this normal?

2. Is the only solution to get an overdrive pulley for the alt?

3. How is it possible that I would get a perfect 0.0ohm reading from the alternator casing to my negative battery terminal, AND a perfect 0.0ohm reading from the alternator output terminal to the positive battery terminal, and STILL get a different reading at the battery than at the alternator? --- When my car is under full load (not including stereo,) I read 12.5 or so at the cigarette lighter (brand new socket,) I read 12.55 directly on the battery terminals, and I was still reading 13.5 on the output of the alt to the casing of the alternator!!! wtf? how is this possible... I could understand if the ground was bad from the alt to the chassis to battery, but I got a perfect reading... can I get a 0.0ohm reading and still have a bad engine ground? (I would assume it would have to be the engine ground to the chassis... but I'm not sure)

bringing the car up to 900 rpm brings output to 13.0v under full load, but with everything off my voltage is at 13.5-14.0, at idle...

Headlights = 9.2 amps
Foglights = 9.2 amps
Blower Motor = 10-18 amps
Engine Fan = 10-18 amps
Headunit = 1 amp
Total = 39.4-55.4 amps
Turning off the engine fan or my headlights bring my voltage back up to 13-13.5

I would think that I need an overdrive pulley...

if anyone has any advice I'd appreciate it.

 

The situation that you are describing is normal and a overdrive pulley for your alternator is not neccessary. If your voltage dropped to about 10 volts or less, then you would have something to worry about

 

GM has several TSB's regarding the problem you describe. As Trickster says you have nothing to worry about. An ohmmeter uses little current for resistance measurements. When you draw current through the wiring minescule amounts of resistance in the wiring cause small voltage drops. The generator only has about 10% of rated output, current wise at low rpm or idle. You don't get close to rated output until you hit from 1500-2800 rpm's. Basically, all cars run off the battery with a heavy accessory load at idle. I posted an article some time ago about this and I found that using a later GM generator(CS-130D) helps this situation. The "D" has a little more aggressive charging curve than the straight 130 in the TG's. You can use an underdrive pulley if you want, but the load of the gen with the load of the accessories may affect idle quality. The engineers took all things into consideration when it was designed.

 

any thoughts on why I would get a 13.5 reading at the alternator, and 12.5 at the battery and elsewhere in the car?

I tried the same thing on my brother's 74 Nova, its got the 65amp alt, and at idle, with JUST his headlights on, it runs off the battery basically... so I tried his battery, got 12.5, and his alternator got 12.5 too...

was my reading just a fluke? (I checked it several times though...)

As far as I know, with a good connection, the voltage reading should be nearly exactly the same at both locations, slight drops at the battery because of resistance in wiring. Not a WHOLE volt or more!

Also is it normal when I'm using full load like that for the voltage to read slightly under 13v even at full RPMs? I'm not too worried about it, it's just that I've gone through 2 bad alternators from AutoZone in the last month.. I hope I got a good one this time, and I just want to know the natural characteristics of the device..

Basically as long as it keeps the voltage around 13 or higher, it's working correctly, right?