Hello,

I just installed a new alternator on my 70.
I noticed that its always warm to the touch even after the car has sat over night. Somthing is not right here. I hooked it up just like the old one.
I also have a new battery. What am I missing?


Thanks for the help!!!!

:beers:

Hello,

I just installed a new alternator on my 70.
I noticed that its always warm to the touch even after the car has sat over night. Somthing is not right here. I hooked it up just like the old one.
I also have a new battery. What am I missing?


Thanks for the help!!!!

:beers:

That sounds like a shorted voltage regulator. It is staying "turned on" and constantly allowing power to flow through the alternator field windings to ground. This is assuming the wiring is correct.

So I should probably replace the voltage regulator?
How can I check to make sure?

Unplug the two prong connector from the regulator and see if it cools down. If it does not, then it likely has a bad diode that is putting power on the stator. If it does cool down ok , then the regulator is suspect.

2 prong meaning the the one long plug with most of the wires running throught it?

First, what kind of alternator does the car have, externally regulated (which is original) or internally regulated? (a popular conversion) If you don't know how to tell the difference go here (http://www.chevelles.com/forums/showthread.php?t=243292).

Most common reason on a externally regulated is stuck points in the voltage regulator.

A common reason on a internally regulated is having the 2 small wires switched.

Its the external original style....

Its the external original style....

Original has a 2 prong plug going into alt. Long plug, just guessing, you may be referring to plug on bottom of voltage reg, 4 wires. Disconnect 2 wire plug on back of alt and see if it cools down. If not reconnect 2 wire plug, disconnect battery, disconnect main power output lead from alt, reconnect battery and see if cools down.

Original has a 2 prong plug going into alt. Long plug, just guessing, you may be referring to plug on bottom of voltage reg, 4 wires. Disconnect 2 wire plug on back of alt and see if it cools down. If not reconnect 2 wire plug, disconnect battery, disconnect main power output lead from alt, reconnect battery and see if cools down.


So do I disconnect the back of the alt or the long plug on the regulator for testing to see if it cools?

Yes, either one. Never do this while engine is running though.

Since its externally regulated, with the key off, disconnect the 2 small wires to alternator, test for power on the small blue wire going to the alternator. It should have none.


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