Battery Light question

[b-wiyeck at microsoft.com (William Yeckel (Lexmark International))]

Just got the 1980 s-pack back on the road again after doing some maintenance and trying to figure out an electrical issue which I though I narrowed down to a bad battery that has been replaced.  All seems fine, car starts and runs fine.  But there is a weird thing going on with the battery light where it will be on for about the first 10 minutes the car is running, then it goes off.

Any ideas what might be going on here?  Maybe some relay that does not kick in until it gets warm enough?

Thanks!

-Bill