so I have a 1972 cutlass I am just getting started with and I have a charging problem... The battery drains fairly quickly, so I tested the voltage with the car on and it started around 20 then over five minutes or so (maybe I shouldn't have been running it that long?) it dropped down to maybe 15. So I figure the voltage regulator is no good - when I open up the alternator i don't think it has a voltage regulator in it? and I read a little bit up on it and apparently this year they had external regulators. so I am not really familiar with how this setup works but i am guessing that the first step would probably be to identify the part, (then test it, and replace if not functional)... however I don't have an adjustable power source so I am not really sure what I would do to test the function, and it is only 21 dollars so I wouldnt have too much of a problem just replacing it and seeing what happens. anyways, is this is it? (see voltageregulator? caption on attached images)
also attached is a picture of the alternator I have and I just want to confirm that there is no voltage regulator in it (alternator titled images)
the other images I was just wondering if anybody knew off the top of their head what these parts were (number titled images) . I am pretty sure one of them is for the horn

 

Your first pic is a voltage regulator. If you have 20 volts charging and then it drops to 15. Both voltages range from way to high, to too high. Normal charge voltage should be between 13.5 to 14 volts on most cars. 20 volts will cook your battery and will damage electronic components. Try unplugging your regulator (once you put the alt back together) start the engine and check charge voltage. If it is around battery voltage. Your regulator is probably causing the overcharging condition.

 

X2, there was probably nothing wrong with your alternator, your issue is with the voltage regulator in picture 6. Facing the firewall from the front of the car just to the left of the distributor, its the square box with the connector that has 4 wires coming off it and the capacitor on top.

 

Would a properly functioning Alternator put out almost 20 volts?

 

Think of it this way - a functioning alternator is capable of supplying more voltage than the system requires, and the voltage regulator "regulates" the voltage to the level the system needs. So I would say that if there is sufficient, or more than sufficient voltage, the alternator is doing its job.

 

Very strange. I have never seen a mechanical regulator that can bring voltage down. They only limit the voltage as it increases. Once the voltage goes past the regulator set point it continues to rise and the regulator can no longer control it. Your alternator does not have a regulator in it. The pictured external regulator is correct for that alternator. I would first suspect a bad battery or a battery with low or no acid. I would also check for bad grounds before I condemed the regulator or alternator. Any one or any combination of the four could cause an overcharge condition (Battery, Grounds, regulator, alternator) . Have the battery tested first then check grounds. Then replace the regulator. You could put a regulator in that alternator if you also add a diode trio and insulate the other screw for the brush holder. Then you can eliminate the external regulator.

 

After rereading, stellar is right I would change the diodes in the alternator. It should not be putting out over 14.2 volts.

 

Somebody's gonna have to explain to me how a bad diode translates to too much voltage output.

 

Shorted diode/s.

 

Explain how that works, please.

In my experience, a shorted diode = low alternator voltage and a continuous drain on the battery when the ignition is off.

One of the charging troubleshooting checks is performing a full field test, where you apply full battery voltage to the Field terminal. This causes the alternator to output its maximum voltage because the voltage regulator is bypassed. If the alternator puts out 16+ Volts, it is working properly and the voltage regulator is suspect. If it doesn't, the alternator is faulty.

Since the OP has an issue with 15+ Volts, I suspect the voltage regulator. It's very easy to check.