86 tqw battery warning light

[frankbauer@scvgvine.com]

for a few days now i have been experiencing a new symptom of a possible
electrical
problem in my 86 tqw - when i first start the engine, the battery
warning light comes on
and stays on until i rev the engine.  once it goes off, it stays
extinguished.  should i start
worrying?  rebuild alternator?  replace regulator?  (anyone tried the
new external regulator yet? eric?)  btw it's got a (coupla months) new
diehard in it.
tia...
frank