Calling all electrical gurus........., my alternator saga continues Options

[East coaster]

I had a strange electrical problem with my 914 and I thought I had it resolved, but now I'm wondering.

A while back, I was driving to work and the car died. I found that the battery was dead. I removed the battery, charged it, and made it to work/home. I assumed my alternator was bad, so I ordered a new alt (alt/reg) and replaced it. I'm running 911 gauges and don't have a volt meter/amp gauge and the idiot light was not working, so I really had no indication while driving other than my stereo would crap out due to low voltage a few minutes before the engine would be affected. This gave a little warning that something was awry.

Once the alt was replaced, things seemed good for about a month or so and then it happened again. I inspected every ground and found nothing. I restricted my driving to my local hood until I figured this out and I finally thought I had.

I fired it up for a drive a few weeks back and it cranked over rapdily and started right up (as it usually does). I proceeded to back out of my driveway and started heading down the street and within 3 blocks (<1/16 mile) it began to die. I reasoned that no electrical problem can take a fully charged battery down that quickly without frying something? I could arc weld with a battery and not kill it that quick! So, I thought the battery itself is the only thing that could cause this symptom.

So, I got the battery replaced under warrantee as it checked "bad" when I returned it and it's been working OK since.

Here's my dilema (after the long winded above description!), I replaced the bulb in the idiot light and now I have a new concern. When I start the car the light is off and remains off until the rpms hit 3800 or above and then it comes on and stays on until I shut the engine off and restart. once restarted, it stays off until I hit 3800 revs. With the light on I metered the voltage and it looks good (14.2-14.4), so it seems the alt is working fine........so what's up with the damn Alt light??????