Hmm, so I have been trying to defeat the bouncing voltmeter for a little while now, but this time I was set out to do it right. A couple of years ago I had broken down while I was out of town and since no one has alternator connectors on hand for my model I had a cheap Radioshack electrical connection crimped onto the wire and it kept a surprisingly tight grip on the pin on the alternator. The 4 pin connection actually only uses the one pin, so it was an easy fix that lasted me quite a while. No one said it had to be pretty.
Anyway, so of course this eventually gave me problems as it went through climate changes. Especially after winter when it began to get warm again. So I assumed this was always the cause of my bouncing voltmeter. So in July '09 I had a put a new alternator and battery in when I rigged up this connection. So I wanted to finally have a stable 14 V and not have to worry about it, so I ordered a new positive battery cable (to alt and starter) and a new actual alternator connector replacement. When I took the current alternator off, the bolt was spinning so I grabbed another one under warranty replacement from Autozone. I soldered the connector onto the wire and electrical taped over the solder and installed everything.
Now the meter is much more stable, but it slowly climbs down at low speeds and idling, especially if high current accessories are on (AC, rear defrost, etc). If I'm going fast (40+) it stays pretty steady around 13.5 V, acceptable in my book. So the question becomes .. what else could be causing the drop? The ground connections looked clean from the battery to the block.
One thing I should mention is I did short the battery out for a second... It turns out you need to be a little more careful with replacement battery cables as they have more metal exposed than the original. So when I reconnected the negative terminal I got a firework show and a car trying to start itself. I electrical taped it up pretty well though and that is fixed. Not sure if this could have damaged the battery or not. It was only for a second, but I know that'* a heck of a lot of current. Fortunately I lived to tell the tale
Ready for suggestions