I have always found the statement that the alternator is "held back" from charging during cold start/ glow plug operation interesting.

So I made a video.

The alternator has 3 wires. The large charging cable to battery positive. The "A" wire is the sensing wire or the circuit that tells the voltage regulator how much output it needs. The "I" wire is the excite wire and tells the alternator to begin charging.

Left DMM is hooked to passenger + and - battery terminals. Right DMM is hooked to driver's side negative terminal and back-probed to the "I" wire on the alternator connector.

About 30 degrees outside, cold start and about 19 hour cold soak. 5W40 oil and the infamous "Buzz" flash for those curious.

<iframe width="420" height="315" src="http://www.youtube.com/embed/sTfun9Rzsuw" frameborder="0" allowfullscreen></iframe>

Interesting, huh? Alternator is commanded to begin charging immediately. I believe it comes down to the fact the alternator is just doing what it can during glowplug operation and once they time-out it can be finally charge as it should.

Josh