6080 electrical problems

I am still having problems with my 6080 im getting 15.1 volts from my alternator right now but i am running it with the circuit board on the dash unpluged because when i plug it in the volts go up to 17 plus and with it unpluged my fuel and temp gage dont work the tach also dosnt work but i think the tach it self is tost any ideas?

Fixed it mostly im still getting 15.1 on the alternator and tach is not working i think i need a new tach any one know where to get one? Parts seem very hard to come across for this thing these days

The circuit board in the dash should have NOTHING to do with alternator voltage output.

The alternator would be a simple Delco 10SI or 12SI.

There's three terminals in the alternator connector, #1 is "excite" and is powered when the key is on, typically through an idiot light, a resistor, or a diode. This power is used to get the alternator charging at initial startup.

#2 is "voltage sense" and likely winds up at the large starter solenoid terminal where the battery cable connects. Sometimes, in simple or "home brew" systems it's simply jumpered over to the alternators' large output stud. This typically works OK but doesn't account for voltage drop between the alternator's output. This terminal is typically "HOT" at all times, key "ON" or "OFF".

Terminal #3 is by itself, the more frontward terminal in the alternator connector. It provides a AC signal from one "leg" of the stator windings to the tach and can be IGNORED if no tach is present, or no working tach is present.

From what you've said, that mucking around in the dash changes charging voltage, I'm gonna GUESS the three wires at the alternator connector have been swapped around or are damages/open/shorted.

So this... unplug alternator connector and check voltages on the three wires.
#1 should have power only when key switch is "ON".
#2 should have power at all times.
#3 (tach) should NOT be powered or have very little voltage. Check and see if the wires are arranged in that order in the connector.

<img src = "http://i167.photobucket.com/albums/u125/27Grainfield/Alternator%20Stuff/Delco_W_tach_zps9gvbvcat.jpg">