87 electrical problems

I have an 87 GT. The guage on the dash is reading between 0 and 8 volts I have tried a number of things and nothing seems to be working, the car has a new alt, new batt,new wires. The only thing that I could come up with is that I have a built internal voltage reg, as well a a ex, and it is passing thru both before it gets to the car, I am new at this, and this is my first stang it is tuf but I love it any help for a rookie would help .......Thanks.

check the voltage at the battery with a dmm if its not 13.5 or more get a new alt