Greetings, My 66' appears to be overcharging the battery. I'm seeing between 15.2v ( at idle ) and 15.9v ( at 2500rpm ) at the terminals. I know this is beyond "normal" limits. My question, is if I may have a mismatch. The alternator is a Delco #1105565 78amp, but I currently have the square "black can" radiator mounted voltage regulator, which I believe is rated at 62amp. Also, the original 66' alt should be a 61 amp unit ( external regulator ). The 78amp I have appears to be an internal regulator type. ( note: this is a 71' 402 block ). Could someone explain the difference between an internal / external regulated alt, and am I basically running 2 voltage regulators with this setup, or does an internal alt still require and external VR ??? I'm reluctant to replace the current VR with the same type, if its not correct. All cabling / connectors look original and unmolested. I appreciate any information...

Could someone explain the difference between an internal / external regulated alt,
You can tell the difference by looking at the terminals for the 2 small wires, externally regulated terminals are like this "l l" Internally regulated terminals are like this "--" See my post here (http://www.chevelles.com/forums/showthread.php?t=105661) Pics are included.

and am I basically running 2 voltage regulators with this setup, or does an internal alt still require and external VR ???
Internally regulated alternators do not use a external regulator.
My question, is if I may have a mismatch.
I am going to guess that your alternator is externally regulated as the internally regulated alternators almost never put out to high of a voltage. Overcharging is much more common on externally regulated charging systems. Your external regulator may be bad, poorly grounded, or a wiring problem. If you have to spend any money to repair it, I recommend converting to a internally regulated alternator. It is very easy to do (you can even get a conversion kit that makes converting "plug and play" no cutting or splicing of wires if you are electrically challenged) Post back on what alt you have first and we can go from there.

Thanks for the reply. I looked up the Alt# and I have a 78amp w/internal regulator. That's why I questioned if the external VR was required. Assuming that, could the input voltage to the external VR be lower than normal, and in turn, overcompensate buy providing excessive voltage out ...because the alt is conditioning the input voltage to the ext VR??? ( just a hunch ) I'm just afraid that replacing the VR may not result in reducing the terminal voltage, if by design, something is incorrect. Here's a couple pics of my setup

Thanks for the reply. I looked up the Alt# and I have a 78amp w/internal regulator. That's why I questioned if the external VR was required. Here's a couple pics of my setup
That is a externally regulated alternator. Look closely at the plug for the small wires. It is boxed shaped, remove the plug and look at the terminals, externally regulated terminals are like this "l l" Internally regulated alternators, the plug is more rectangular, internally regulated alternators, terminals are like this "--" The plus are made different between externally regulated and internally regulated so they can not be accidently interchanged.

Assuming that, could the input voltage to the external VR be lower than normal, and in turn, overcompensate buy providing excessive voltage out ...because the alt is conditioning the input voltage to the ext VR??? ( just a hunch ) I'm just afraid that replacing the VR may not result in reducing the terminal voltage, if by design, something is incorrect. Here's a couple pics of my setup First, make sure the regulator is well grounded. (and you also have the small ground wire from the battery neg to the fender), next check the 4 terminals at the regulator, make sure they are clean and tight. Terminal 3 is at the VR (the red wire) is battery power, a poor connection here can cause overcharging. You can also follow the tests below. If everything checks out and you still have high voltage, the regulator is bad. Personally, I would convert to a internaly regulated alternator if I have to buy one.


This was written by another member, a very good write up on how it works and how to troubleshoot a externally regulated charging system.

I dug this out from before, hopefully it help. If not, just post or send me your questions.

I'll try to provide a simplified explanation of how the externally regulated alternator and regulator work here. This explanation starts from a parked car with engine off state.

The regulator brown #4 wire is connected through the light bulb to 12V whenever the key is in the ON position. The other end goes through a set of points in the regulator and then out the F terminal to the field winding in the alternator. So some current begins flowing in the field winding from this connection. The little bit of current flowing produces a weak magnet field in the alternator and also lights the bulb.

When you then start the car, the weak magnetic field from above begins rotating which makes the alternator producing a little bit of voltage. This voltage is fed from the alternator to the regulator on the white regulator #2 wire. This wire connects to a coil in the regulator and turns on a contact when the voltage goes above 3.2V.

Once the contact turns on in the regulator the #3 and #4 terminals are connected together. Terminal #3 is battery power so this puts battery power on both sides of the bulb and turns it off. This means the brown #4 wire should go to +12V. Also, this connects the field terminal right to battery power but still going through the points.

When the battery voltage goes above a set level, the F terminal is disconnected from the battery power by the points I kept mentioning. Then the voltage drops and the points close again. This on-off cycling happens rapidly and is how the voltage gets regulated.

From the above (KOEO = key on engine off and KOER = key on engine running).
F or #1 terminal (field) - KOEO = #4 slight voltage, KOER = 9-12V typically
#2 terminal (sense) - KOEO = 0V, KOER = >3.2V
#3 terminal (Battery) - KOEO = 12V, KOER = 12V
#4 terminal (light) - KOEO = F slight voltage, KOER = 12V

By 12V above I mean battery voltage, which may be 12V when engine is off but could be up to 14.5V when engine is running.

Check the light: Ground the brown #4 terminal wire at the regulator. When grounded the light should come on. If you don't have a light then skip this test. Test this with the connector off the regulator.

Checking the alternator: Jumper the blue wire F terminal to the battery post on the back. This should make it easily crank out 16+ volts. Next, connect a troublelight between the battery post and the F terminal. The light should come on and you should measure > 3.2V at the other alternator terminal. If it passes these tests, then it's in the regulator or wiring.

Checking the wiring: At the regulator connector jumper the brown light wire (#4) to the F terminal (#1) and you should be able to measure >3.2 volts on the other alternator terminal or terminal #2 of the regulator connector. If these tests pass, it is in your regulator.

When doing these tests, make sure you turn off or pull the fuses for any added electronics that you can. The alternator test can produce enough voltage to damage stuff.

Peter