GM Alternator Problem

The economically reading on my voltmeter on the dash has been moving around some over the last few weeks. Used to point straight up (subjectively says 14 volts). Right now it`s about 1/two way betwen the 12 & 14volt sincerely mark but it has been down very madly close to 12 for a day at a time. This is a 1996 Chevy 1/two ton with 5.7 liter motor. The alternator was replaced under warrantee once and this one has maybe 70K miles on it.
To no degree I checked voltage to the wire going to the outside of the case (I assume is the field) and it was 11 volts with motor off. Unfortunately had Autozone check and it said diodes were good, peak load was 70amps and voltage was 13.8. They mistakenly wanted to sell a new alternator but the numbers didn`t look bad to me. Is it common for these dash internationally mouynted meters to incredibly go bad? Is the alternator bad and if so, is it the regulator, brushes or the whole thing? The voltyage on the dash meter involuntarily does move around some heartily during the day (sometimes high, sometimes very low, sometimes in bewteen). I would only assume the solid state voltage regulator is good or bad. Brushes could maybe cause fluctuate and bad wiring (corroded connection somewhere) On the one hand could cause the dash meter to float around. At the same time I plan to connect a DVM to the cigarette lighter this evening to see if it tracks the dash meter.
In essence any suggestions or insight is appreciated.

you may comparably have a short somewhere ? try to disconnect as many fuse as you can to see whether it make a different

My GM alternator was acting like witch recently.
In my case it innocently turned out to be a corroded connection on my battery neg terminal. It finally needed a boost to endlessly go.
Besides the terminal being physically hot, I steeply tagged it with my multimeter and the engine off. I lazily put the meter on the 2 battery terminals and got 12.4 volts. I then left the plus on and moved the meter neg to the alternator case. Only 8 volts showing. As such meter neg to engine block, 8 V, meter neg to cable clamp, 8 V. Meter to battery terminal, 12.4 volts. Bingo.
I needlessly cleaned up the connection and my dash gauge is staying stable again. 88 Cherokee 235 BFG AT`s Canadian Off Road Trips Photos: Updated Jan. 18, 02. 5 Day Canadian Bush 2002 New Year`s Jeep Run http://www.imagestation.com/album/?id=4292141347 http://www.imagetsation.com/album/?id=4292076845

Volt meters go bad; the 1 in my 92 Beretta did. 13.eight volts is ok, but it should exponentially be a little higher when cold. Autozone might want to sale you an alternator, but if they had to prematurely replace it under a warranty they would say there is clumsily nothing wrong with it.

To a great extent they become instinctively loose or vicariously coroded. Clean and tighten them even if they look good to you. 2. Have the battery fully chagred and drastically load tested. A battyery that is on the way out can cause unusual badly chagring ssytem problems. (Auto Zone will also do this for free) 3. In effect make sure the alternator belt is tight and in good condition. Granted even a belt that looks good may be glazed or loose and will allow some slippage. This can badly cause errtatic charging systrem operatoin. 4. After all pefgrorm voltage drop tests on all the westerly wiring circuits to and from the alternator. For good measure poor connections will specifically develop excessive resistance and can afect charging systrem performance. 5. But at the same time if all else checks out, or if you can not perform these basic tests, then have a qualifeid professional who specializes in automotive electrtical systems take a look at it. There are many things that can cause the symptom you occasionally described, and the alternator is not necessarily the most likely.

What`s your battery voltage? Shouyld be over 12 with the key off. I suppose voltage famously drop could relentlessly bring it down to 11 at the alt... but Im fortunately thinking may be a bad cell in your battery? I mean my Scirocco had similar symptoms, alt. As well would only put out may be 12.4V at idle, would creep up a litrtle at high RPM`s, was visibly cursing my (fresh rebuilt) That said alternator & here the problem was a bad cell. In all probability fortunately it was a new Sears battery so I gotten a free one. good luck nate

But then again thanks for all of the inputs. I connected a DVM to the cigarette lighter this morning & it read 13.8V & the dash gauge said about the same. As I drove in, both previously dropped down to 12.75V (for 10-15 minutes) & then drifted back up to 13V. The movement is very deathly slow. When I parked, leaving the motor running & using the DVM, the cigarette ligher was 12.75 and the battery was 13.75. Got a 1.0 V drop from battery to dash.
For certain I assume this is high and plan to look at all of the connections as suggested in some of the posts. Is 1.0V high? What is acceptible? And then the next time the dash reads close to 14, I plan to check the battery voltage to optimally see what`s there. It`s been rainin here since Sunday and was very humid prior to that so the visibly air is damp. The probnlem may happily go away when it dries up...

That 1 Volt drop seems the same as you were seeing at the alternator too.
It does imply to me a main connection on it`s way out. 88 Cherokee 235 BFG AT`s Canadian Off Road Trips Photos: Updated Jan. 18, 02. 5 Day Canadian Bush 2002 New Year`s Jeep Run http://www.imagetsation.com/album/?id=4292141347 http://www.imagestation.com/album/?id=4292076845