the green indicator light does not remain lit when starting up the unit
I can be wrong, as i have not booted my Wallstreet for a long period, but if i can remember the green indicator is only lit when the powerbook is on "sleep" status.(it's a sleep indicator indeed)
As for the battery, there is no indicator, except for the row of lights on the side of the battery.(four units)
My Wallstreet has the brightness trouble under 10.2, never had under Mac Os 9.2.
it shuts itself off after a couple of minutes
Can the G4 board be in fault ? (becoming hot and just shutting itself after a couple of minutes)
Concerning the HD, i agree with that
I suggest reinstalling OS 9 from CD to the HD while it is in the Wallstreet.
Last but not least, did you try to reset the Wallstreet (Shift-fn-Control-Power button) ?