My brother owns a 1986 Z-28 (Tuned Port) and has had some difficulty with his charging system. He replaced the battery and tested the alternator (which they say is charging at 12.6 volts), but he's still only reading 10 volts at the gauge. He says he's checked his wiring, but still can't figure it out. Any help would be appreciated.

 

The alternator has to run all the electrical accessories plus charge the battery so it needs to be putting out at least 13.8volts, even better would be 14.3volts. So the 12.6 volts your getting now is not acceptable. Rebuild the alternator or get a new one.

 

If the alt is really only putting out 12.6V, then it's toasted. If so, replace it. One thing I noticed, though, is that with good (what I would call 'proper') ground & supply line runs, my alt voltage jumped up about a full volt (and more). I was getting about 13.4 all day, every day. I ran 0 AWG from the engine to the chassis to the battery (-) and also ran 0 AWG from the alt output to the battery (+) and now register 14.7+ on my meter.

Chances are you either have a totally dead battery that's dragging the alt down or a bad alt.

 

Phlaxus makes a good point about upgrading your main battery + and - wires.Going from the sometimes factory 6ga to 2ga wires gives a cleaner path for your battery to recharge and provide power.Nedoss is right about the 12.6VDC showing your alt is toast.You want a minimum 13.3 but no more than 14.3 or you'll cook your battery.
And another thing fully recharge your battery when you install the new alt.Alternators were made to maintain a charge not recharge a dead battery(you can burn up the diode pack/voltage regulator doing this).

 

Also, many wires under the hood are copper-clad aluminum [this includes the large-gauge wires]. I bet that with all that engine rocking, some strands of wire will fray.

This is obviously not a good thing. Also, aluminum wire corrodes around each crimp-connector.

Seth