Oldsmobile/Buick Repair: Olds Silhouette Electrical ?, drive pulleys, battery connections

Question
They had you in the Olds/Buick repair category but after reading your profile, I'm sorry if I'm wasting your time asking a question out of your area.  Anyway,  I have a 2000 Olds Silhouette with low miles(45K).  All of the interior and exterior lights (dash, head and tailights, dome lights) all flicker very badly especially when the car idles.  When the rpm's increase for instance while driving, there is less of an issue.  I was wondering if you have any ideas before I blindly believe what the dealer tells me.  I have come across one other occurence of this reported on the internet.  The dealer in that situation replaced the alternator to no avail.  BUT when the ground bolt on the alternator was replaced, the problem was solved! One other thing I've noticed is that the van rolls backward on a hill IN GEAR!  Could these problems both be related to the van idling too low?  It idles about .5 to .75 on the RPM gauge.  Any advice or ideas would be much appreciated and in advance thank you for taking the time to answer me.

Regards

Answer
Hello Damian,
An excessively low idle could cause that, but usually not unless it is in conjunction with a poor ground somewhere.
Check basic things first.
Make sure the battery connections are clean and tight, on BOTH ends, including where the ground connects to the engine.
Then make sure there is a good ground from the engine to the firewall/body, as well as any other ground wires.
Disconnect the battery for a few minutes while cleaning the contact area of the cables, and check the voltage of the battery. Should be about 12.1V or so.
After all the cleaning and tightening, check the voltage after starting the engine. Should be about 14.
If the blinking, or is it more of a brightening and dimming, only happens at low idle, I would have it where the blinking happens, and temporarily remove the belt from the alternator and other drive pulleys, and start the car again, only running it long enough to see if the blinking happens without the alternator. You could also just disconnect the alternator output wire to see that, but to avoid accidentally touching the wire or a wrench to ground, you should probably do that with one of the battery connections unhooked.
Then run the car, and the only purpose of that is to see if the alternator is causing the blinking.
If it is, then take the vehicle to a shop that can test the alternator while it is on the car, but be sure it includes a diode test, not just a voltage test.

Obviously, the ground wire/bolt at the alternator should be checked while the others are being checked, but I can't immagine that you haven't already done that.

Not working on Silhouettes, I don't know what the RPM should be, nor if there is an adjustment. Too low could allow it to coast backward on the hill. What does it do if you maintain just a little bit of throttle, like 1.5?

It is remotely possible that all of the problems are related, but just doing those basics needs to be done anyway, and could even help.

Sorry if I seem to be vague, but these are general things I would check and do to any vehicle.

Van