Sorry about the multiple edits on this post...
I just realized that the clicking is happening because the HVAC is set to defrost. I understand it is designed to have the AC kick on during defrost, although I'm not quite sure why. So I guess that is normal as the compressor cycles on and off.

Still concerned about the battery voltage though... I'll check it with a different meter and report back.

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Hoping for some help here. Just my luck to have an issue crop up just a couple of weeks before the Wine Country "Vine Run!"

I just recently noticed a change in the idle speed that is coincident with a loud clicking sound coming from the engine bay. Each click is accompanied by a 100 RPM shift up or down between 800 to 900. I have not been able to isolate the location of the clicking but it seems pretty loud with the lid up. Sounds like a switch or solenoid clicking on and off?

1988 GT, automatic trans, 3.4 L, A/C.

(I have no idea if the issues are connected, but about the same time as the issue above I also noticed that the voltmeter jumps close to the red area upon startup but settles back down to normal range after just a few miles. I used a voltmeter to check the voltage across the battery terminals at idle at 16.5 VDC and with engine off at 15.5 VDC. Seems high to me?)

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John Wayne as John Bernard Books in The Shootist...
" I won't be wronged. I won't be insulted. I won't be laid a-hand on. I don't do these things to other people, and I require the same from them."

My rides...
1988 GT with a 3.4L V6 automatic
1987 GT stock (with added stripes)
2006 Harley Sportster
'cause I love the twisties on two wheels or four.

[This message has been edited by Rsvl-Rider (edited 03-16-2018).]

That voltage is too high. You will damage your battery and possibly your electronics if that keeps up. I'd expect bulbs not to last long. 14.4v is generally the limit. You might see a bit higher at the alt, but not by much. 13.8v is what a lead acid battery can sustain indefinitely.

Is your volt meter accurate? Your battery should sit at about 12.6v after it's rested for a while, say an hour or more(though it should get there n a few minutes). Doesn't have to be on your fiero...just use that voltage reference as a means of checking the calibration on it.

If you're really charging at 16.5v...you probably want to check that the voltage reference wire going to your alternator is hooked up properly and not corroded. Check what voltage it's getting at said terminal. If that's ok, your alt's regulator is screwed. Take it in to be tested to confirm and presumably replace it.