Are you turning on A/C or other accessories?
MZ

You don't mention the mileage, but guessing it's around 150K miles or so the
alternator brushes are probably worn out. Often they are worse when warm,
but mostly that is a marginal difference. Brush trouble shows up in the
early stages as intermittent charging, and a '90 might be early enough that
the warning light won't tell you anything is wrong. More recent Hondas use a
separate sensing circuit.

If you are seeing the voltage pop up and down, gradually becoming more down
than up, you are probably seeing the brushes make their last stand.
Replacing the brushes, assuming you can obtain them, is a cost-effective
approach. See Elle's web page on that at
http://home.earthlink.net/~honda.lioness/id13.html - her site is tailored
more for Civics but the principles are the same.

Avoid aftermarket rebuilt alternators. They have earned a reputation for
poor reliability.

Mike

"RandyCamp" <hrmajor@gmail.com> wrote in news:1175119290.082458.281130
@p15g2000hsd.googlegroups.com:

It's bad. Replace the alternator. Voltage at idle should be 14.4V.

If you choose an aftermarket reman, it WILL fail in just over a year.
Guaranteed. It does not matter where you buy it, NAPA, AutoZone, Kragen,
they're all lousy.

If you spend twice the money to get a genuine Honda reman, you can install
it and forget about it.

There is a slight chance the brushes are worn, but this normally manifests
itself as a flickering charge light.

--------------------------------

Any time the alternator circuit is discussed, it's probably a good idea
to SEARCH google and understand the Honda ELD, since it affects any
measurements and might fool the AutoZone people, or yourself.

'Curly'