Chevrolet Repair: 96 Silverado alternator, fuse block, volt meter

Question
I have a 96' Silverado.  The dash readout on the alt. reads between 10 & 13.5 volts.  by this I mean it changes alot.  It may be reading 13.5 then suddenly it will drop to 10 or 11.  It may stay there for a while then go back up. I checked the cable going from the alt. to the battery and the Vdc was reading 14.2VDC at the same time the gauge was reading 10.  The battery volt. was 14.
I'm not sure where the smaller wire from the alt goes. Is this the wire that gives the readout on the dash?  I tried to get it off and check it there but it is hard to get to it w/out removing the alt.  Could this problem by chance be just the dash gauge?  If so how do I go about hooking up a under dash gauge as a replacement.  I would greatly appreciate any help that can be given.
The alt. that is currently on the truck was bought at a dealer in the last 6 months and installed myself.

Thanks
BB  

Answer
Hi Bruce,
Probably the easiest way to hook up an under dash volt meter is to just run the + wire to the fuse block under the dash, and connect it to an accessory terminal. That way it will only be reading voltage when the key is turned on.
The indash gauge isn't all that hard to change, and could just be loose or dirty connections. It just pushes into some clips for contact, and just wiggling it some could fix it. Either that, or where the wire harness connects to the back of the instrument cluster.

Van