I have a question on wiring. 72 Chevelle converted to internal regulator CS (I think) alternator. The Alternator is the latest GM alternator that is used in these conversion. I cannot recall the designation because I did the work years ago. I think this generator is 2 generations later than the one used on the 72. It has a black section between the ewo case halves. I hate describing things like this but I am short on time and I wanna get going on this repair. The questions are as follows.

Hpw do I test the output of this thing? Voltmeter probes go where?

When the fans go on (twin electric Derale) the voltage at the dash board volt meter goes down ...well below 12 volts when the fans are off the voltmeter jumps to about 12.20

Votage testing at the battery with the fans off engine running shows about 12.24 and the battery with all the stuff shut down shows about 11.73 when the motor is not running. This says that the alternator is putting out something but I think it is not putting out enough.

My reason for the question. I need to determine if the battery is hosed or if the alternator is not putting out sufficient juice. I think possibly the battery is not up to snuff but don't know enough about electronics to be sure . This might be the alternator OR it might be the battery. Certainly the fans are putting out a serious load but if I take them off line and out of the equation the car still does not seem to be behaving right.

I think I should see around 13.xx volts when the alt is charging properly and the engine is on but I never do. If the alternator is putting out sufficient juice could the voltage at the battery read low because the battery cannot accept the output of the alternator? I think the alternator was working OK a few years ago when the car went to sleep. Now I am expecting to see 13.xx at the voltmeter when the car is in immediate post start up mode and the fans are off but the best I get to is 12.3

The big alternator is in the car to assure that I can run the fans w/o killing the battery and based on what I am seeing this is not gonna be the case.The alternator appears to not have the suds to keep up with the fans. I am not sure if it can even keep up with the car w/o the fans. On the other hand perhaps the alternator is OK and the battery is hosed?

Ay comments apreciated. Thanks a lot

Battery should be 12.6 with engine off, key off. Fully charge your battery before doing other testing. If it won't take a charge, it's going to need to be replaced. And you could still have a charging issue to resolve.

I think I have it figured out. The CS alternators have to have a circuit that "excites" the alternator....essentially it tells the alternator "Hey wake up you have work to do".

The circuit on my car is disconnected. That circuit has a bulb in it and a diode. The diode prevents running on after the key is off. The purpose of the bulb is to present a load to the alternator / regulator excitement circuits. Once the alternator / regulator senses the load from that bulb the alternator / regulator is "excited" into action. I totally forgot that circut was disconnected when I removed the dash and I totally forgot to reconnect it for todays instrument cluster test.

I think that the problem is solved but I have yet to reconnect that circuit to prove that I have the right fix in mind. Gonna look at it tomorrow but I think I have the answer.

Thanks for the reply...if I am right you are also right. I do have a charging issue and the issue is (hopefully WAS) an unexcited alternator.

Now if women could be dependably and repeatably "excited" by just connecting two little wires....................