I installed a new alternator and voltage regulator. I was told that you did not have to do anything to the new alternator to get it in charge mode, but I am only getting 12.5 volts output. Voltage regulator is good. Any suggestions of recommendations

Check the bulb in the dash....it may be part of the circuit to excite the alternator..

Could be lots of things.
You can ground the signal to the alt from the VR so alt goes to max output.
If you get ~13.5Vs then vr or grounds are bad.

Oh, and you should polarize the alt even if you were told its ok.

Thanks,
Electrical is not my strong suit and not sure how to ground the signal to the VR?

You could even have a slipping belt.

How are you reading the 12.5 volts.... gauge, meter?
Where is it connected?

I have a voltmeter reading from the positive and negative to the console VDO meter

You must read across the battery. Measure without the motor running then compare when the motor runs. Rev the engine a couple of times then measure.

Assuming your alternator and VR are good, it sounds like you're not getting the alternator going. The armature (rotating part) needs current through the GEN light on the dash. Make sure the GEN light lights up when before cranking.

And as mentioned before, measure voltage across the battery. The VDO gauge can have significant voltage drop WRT the battery voltage.

Does the Gen light come on with motor not running? You need it to make the circuit. May be as simple as replacing the bulb. Also NEVER use a LED for this.
mark

The VDO gauge must be way out of calibration as my voltage across the battery with and without the engine running is about 13.5 - 13.8 as the gauge just reads 12V

It has to do with age & corrosion. Your wiring is 40 years old and the ground plane is just a bunch of rusty spot welds. Vehicle wiring is barely adequate for the circuit amperage. Oxygen starts to breakdown the copper at each connection point. There is enough resistance in the system to eat up 1V as voltage drop.

The factory volt meter was never designed as a scientific instrument. It should be viewed as a relative measurement of voltage. Always measure at the battery. Rev the engine to 1500 rpm and ensure the voltage is slightly higher than idle. The alternator will usually not charge below 1200 rpm.

Why I asked how you were measuring it...13.5-13.8v is perfect, nothing wrong with your charging circuit.

Shouldn't there be a bigger difference in voltage between checking it with the engine running and not running? Close to 14 volts with engine running and closer to 12 with it not running?

I really appreciate all the feedback. First, all my harnesses are new, all ground are clean and good, no LED light in the volt meter, No Gen light at or above idle, Starts and runs at about 1200 RPM then settles down to 650-700 RPM (idle was higher until I took the aux air valve apart and repaired the stuck valve). So maybe I do not have a problem. I am taking it on its first shake down run after three year restoration project, as soon as I get a clear dry day. Then its just a matter of adjusting and tweaking all the little gremlins. Stay tuned!

The little voltmeters that plug into the cigarette lighter socket also can be used to double check the voltage.Click to view attachment

It’s nice as you can easily move it between cars if needing to check other vehicles.