I purchased my father's 1986 Vette coupe. He owned it for the past 20 years and hardly drove it because he has had two knee replacements and frankly has a hard time getting in and out of it. It has 52K original miles and is in really nice shape. Hooker headers and aftermarket exhaust (I forget the specifics...Not straight pipes but certainly better than stock). He also has an underdrive pulley which may be causing some electrical problems, I'm guessing. While driving at night, the dash intermittently fluctuates in brightness. I wouldn't call it a flicker. In addition, the other day the a/c would not work at all unless I turned the fan down to 7 or below (it has the digital climate control). We did put a refurbished climate control module in because the previous one failed and that seemed to fix the a/c until recently. At idle, the voltmeter is only registering 11.3-11.4 volts. While driving it improves at higher RPM but obviously something is going on. I'm going to have the alternator and battery tested tonight. Anything else you guys can think of? If I decide it's not worth it and go back to a standard pulley will I need a new belt? Honestly, for a modest engine performance boost I'd rather not sacrifice stability and end up with a dead battery or worse. Thanks in advance and I look forward to participating in this awesome community!

 

check out the conversion to the CS144 alternator instead of CS130, i fitted one to my 89 Coupe and it has eliminated all of the low voltage issues, apart from filing down one of the upper mounting lugs to fit the bracket on the 89, it is a drop in replacement, went for one for an 1997 LT1 Camaro got it from Rock Auto.

Here are some photos of the new installation

 

When I ran an underdrive crank pulley it required an overdrive alt pulley, still voltage was not entirely up to snuff.

If you change pulley sizes it will require a new serp. belt.

 

Well, I had the battery and alternator tested. Both weren't terrible but not perfect. He wasn't sure if one was causing altered performance of the other, but I figure the battery is 7 years old and the alternator is 34 years old and they're relatively cheap so I am replacing them. I ordered a 105 amp alternator from Rock Auto that will be here Friday. The parts stores in town didn't have my alternator in stock. I'll see how things go after that. Thanks

 

I have an 86.
i upgraded to an alternator like the previous poster.
it charges at idle, and every summer, i do not have to overhaul the alternator when it gets so hot it pops the diodes.
If you bought a rebuilt alternator, there is something you should look for.
when the overhaul shop takes it apart, they cut the field wires and pull it apart.
when they put it back together, they use a crimp.
its not a real splice.
its a ring. They put all the wires in it and smash it.
it becomes a loose connection with hundreds of heat cycles, expanding and contracting.
it loosens up and becomes a hot spot. Heat is because of resistance.
your old alternator might just have that crimp.
i also have a factory pulley if you want to rebuild your old alternator, and return it to factory.

 

An under drive pulley isn't worth the trouble in the street. I would almost bet that if you changed out the pulley the low voltage would go away. The battery is older and the alternator is original so maybe its better to replace them.

 

I might have an alternator overdrive pulley that will fit. Bought it cheap at Summit and then later realized it would need to be machined to fit my LS swap car. Supposedly it fits your style alternator but I would need to some pictures of the pulley by itself before I send it to you. 6 rib belt?

 

That CS-144 alternator needs a rear brace...

 

 

So, I replaced the battery and alternator. I ran into a bit of a problem because the pulley on the new alternator was slightly smaller. I thought the difference was minimal enough to not cause a problem and the tension on the serpentine belt seemed okay but there was just enough slack in the belt to cause a squeak so I swapped out the pulleys. Now, I'm getting over 12 volts at idle and 14+ volts just cruising around, which is a huge improvement so there's no doubt in my mind the alternator was bad. However, the A/C problems persist. If I set the temp down to the lowest setting ("60"), I can feel cold air coming out of the vents but only if I set the fan speed to "5" or lower, and even at five it is very very minimal. You have to put your hand right up against the vent to feel it so for all intents and purposes it is not enough to cause a measurable cooling affect in the cabin. Is it the climate control module, or something different? Where do I start? Thanks!