Check for a momentary drop in rpm when you brake. Sometimes the IAC valve gets dirty and this drop in rpm effects the charging. AC Delco site lists 90 as the cutoff point for alternators. 91 and up are not the same unit.

Yes, there is a momentary drop in RPM - sorry - but what and where is the IAC valve - I'll check it...

ok - Air Intake Control valve - location?

Thx
Tom

Same thing here... cold is 3/4 on gauge. If I have lights, heat, stereo [500w system] on at idle, it drops down to about 1/4 on the gauge, everything dims, car barely idles. Otherwise, it'* fine, but anytime lights come on initially it puts a big load... moves about two needle widths with turn signals and brake lights. 13.9v at idle, 14.2 at 1500+. Alt is giving out, but still works so it stays. All my cables are in great shape, cleaned extensively, grounds included [engine compartment grounds at least], so it'* not a cable problem. And the voltages are the same if testing at the back of the alt itself. I have a good battery as well.

Brand new battery and newish alt and my guage will bounce when I use turn signal or apply brake.

i've got a brand new alternator on my 89. the garage checked the battery and said is it putting out properly. my guage runs about 3/4 and if i'm in city driving with a load on it,(lights, defrosters, stereo) it will drop to about half at stop signs. i also get a little "ticking" motion from the guage when i'm stopped to make a turn and the signals on. all i can go by is my garage. they've tested everything and said it charges as it should. i just figured this is maybe just the nature of the car.

I,ve read this on another forum, but they said it will help with dimming lights. they called it the big 3. you can just add the wire or you can replace them, they recommended adding the wire. but any way the battery ground should be replaced. the engine ground to the frame, and the altenator to the battery wire. they say to use at least a 2 gauge wire, or if your can a 0 gauge wire. i plan on doing it to my car. also just woundering do those 140 amp altenators fit in a 88 sse?

i have a 160 in mine..
and you should start a new post.. not dig up old ones.
just an fyi...

All your drop voltage symptomas you described are exisitng since almost day on on my car.
Well, nothing new under the bonnies sun. I own a 1988 SSE since new, and I have to tell you that condition is a typical GM wrong design issue.
This problem exists since day one and let me tell you that 105 amps alternators will need to be changed religiously every 2 years.
In 2004 I got stucked on the road with a dead AC/DELCO REMAN 105 AMPS on a sunday and the local garage where I was stucked could get any fresh replacement alternator and managed to install a used 140 AMPS alternator from a WRECKED Buick Lesabre donnor (1993 i think) and it fitted to allow me to return home.
I kept the 105 amps dead core and brought it to a local alternator rebuilder and asked them to make sure it delivers 140 amps...like the buick.
The battery gauge indicatorIt still does the flicking when I touch brakes or turn flashers on a traffic light but the charging system is quite more prompt to recharge the draining
of energy.
Another trick I found is to plug a solar panel 5.5 amps that I plug into the lighter socket
when I do not use the car on a daily basis.
It keeps the battery very strong all the time.
I should had done this long time ago.
On 1988/1989 model...you will have to live with the flicking because it a design problem
from GM. They prpbaly figured out how profitable for them is it to sale Alternator replacement than fixing the problem with a service bulletin since day one.