While cruising today, my voltage gage which normally registers about 14v, jumped to 18v.  At the same time my temperature gage crept up from the normal 200 to about 240.  At idle, the gage reads 14v, as I accelerated (slowly) to 15/20mph the gage moves to 18v (could be higher but the gage tops out at 18).   According to the schematics, both gages share the same circuit so this does not concern me - just an observation for you......My battery light did NOT come on.  Additionally I followed the diagnostic steps in the GM Service manual and it points me to the Generator.

My question...does this sound like the voltage regulator is bad?  Anything else I should check before I try to replace the regulator?

thanks (appologies if this has been covered before but I could not find a post/discussion relating to the voltage gage)

It could very well be the alt., but before replacing it, check to see what it is actually doing. Put a voltmeter on the back of the alt., on the large, red terminal, and see what kind of voltage is there, at idle, and at higher rpms. If the voltage is high, then the alt. repair is called for. If not, then you have a gauge problem, most likely a bad ground.
I've never been a fan of factory alt. gauges. A lot of them are just not accurate. A voltmeter is the best way to determine if the alt. is working properly. Also, I've found that most 12v lights don't like 18v for very long!! If the voltage is indeed that high, then the light bulbs are not long for this world!

The voltage regulator is inside the alternator.  It's not really to difficult to replace.

But before doing so, make sure the system is actually at 18 volts by using a meter at the Batt connection on the back of the alternator.  If you do have the 18 volts, check the connections to the alternator and the grounds.  Even with the alternator bolted tightly in place, you can lose electrical connections due to corrosion at metal contacts. Also check all the battery cables and connections.  A loss of connection to the battery caused the regulator to lose it's reference, and voltage can then do weird things.

Thanks guys....will do your checks first and see what the output voltage is.

The voltage regulator went out on my 79 one time. I noticed the radio would cut off when I pulled out from a stop sign but would come back on when I let off the gas and stopped. I went down town to wash my car at the quarter car wash. When I pulled in, I could hear my battery boiling. I lifted the lid on the battery compartment and there was electrolyte all over the battery. I got back into the car and drove it home and watched the gauge, it pegged whenever I touched the gas and dropped back to normal when I was idling.

Check the voltage at the back of the alternator, like everyone is suggesting, and be sure if the regulator is bad to change the regulator or alternator before doing any driving. It can ruin the battery quickly.

18.37 volts off terminal 2.....on my way to get a voltage regulator and try that before replacing the entire unit....although 22 years old, it only has 29000 miles on it so I would expect the generator to still be good.

well...two hours later I have the generator back in the car with the new voltage regulator ($20 bucks).  I will have to wait a few days until I can get some help pulling the generator tight and tightening up the two bolts (don't have an impact gun so I need someone pulling on it while I tighten with the socket wrench).

 

Go easy on how tight you make the belt. You don't want to get it so tight that it ruins the bearings. You should be able to hold the alternator tight enough to make the belt tight while you tighten the alternator. 

Its in, and crank'n out 14.8 volts....life is good again