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Testing a charging system

Kern Dog

Life is full of turns. Build your car to handle.
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My Brother in Law's 72 Duster has been at my place since 2007.
He recently said he wants to use it as a fair weather Daily Driver at his place in Phoenix AZ.
He likes these cars but has always had me around to guide everything and advise him. Once he takes the car, he will be on his own.
I'm trying to periodically when time permits, work on this car to ensure that it will be safe and reliable. Today I decided to check the charging system. The gauges are not working, that is on the list of things to do. I suspected that the alternator might not be charging so with the engine running, I removed the negative battery cable. The engine shut down. I should have checked the voltage with my meter but I did not, I just grabbed another alternator from the shed, a nice clean one with a rebuilders tag on it. It showed a 13.9 volt reading at the alternator and the battery was at 12.8. I pulled the negative cable and it shut down again. There is a ground cable from the block to the firewall. Why would the engine still stall if the alternator was putting out the right voltage?
 
1.1v drop between the alternator and the battery.
Maybe high resistance in the amp gauge?
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The regulator is probably shot and there may be short or some other load on the system which may explain the variance.
 
That is not how you check. A voltmeter reading of approx 14.0-14.5v is in the ball park. Actual output needs a load applied and a amp reading.
Doug
 
That is a good test for a Generator, not so good for an Alternator, since the take juice to make juice..
I would throw a new Regulator at it, clean the mount, firewall and regulator for a good ground and move on to the gauges..
 
The alternator is charging as it's putting out 13.9 volts.

Sounds like a bulkhead/wiring to the battery issue unless there is a huge amp load in the car itself.
 
Put ac in it for him so they don’t find him somewhere cooked. Who is going to deliver it?
 
HA!
I'll probably have to tow it out there!
 
Do the same test you tried earlier but this time lift the positive cable off the battery, it should stay running.
 
Your transmission is shot and you need news tires.
 
But I only brought it to you for a oil change.
 
Do the same test you tried earlier but this time lift the positive cable off the battery, it should stay running.

Nice catch! I missed that...of course it will shut down when you remove the negative or ground reference. Duh!
Even so, the unregulated voltage from the alternator should be higher depending on the rpms.
 
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