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1973 Spider; the daily
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Discussion Starter #1
On my 73 spider my generating light comes on with the key in the on state with the car not running. Light remains on when the car is running. So assuming there is no short would that mean my alternator regulator is bad. How could I test it. Also is the alternator regulator the black box on the backside of the alternator. Thanks for all your guys help.
 

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Yes, sounds like your alternator or regulator isn't working. The simplest way to diagnose this is to put a voltmeter on your two battery terminals, and measure the voltage with the engine off and again with it running. You should see numbers like 12 V off, 13.5+ V running. If the voltage remains at ~12 V with the engine running then either the alternator or the regulator (or the wiring between them) is bad, but it's harder to diagnose which is the issue. Taking both components to an auto parts store and having them test them is the next step.

On an original '73 spider, the regulator is mounted ahead of the battery; not on the alternator. I can't explain what that "black box on the backside of the alternator" might be. A picture would help.

It is possible that someone replaced your '73 alternator and regulator with a later model, internally-regulated alternator. Those have sort of a black thing on the backside that is the regulator.
 

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1973 Spider; the daily
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Discussion Starter #3 (Edited)
The voltage off the battery without the car running is about 12v. With the car running it seems like there was less voltage about 11.8v. I found the regulator and it looks to be original. Is there some way I can definitely check and make sure it's the regulator. Here's a picture of that black box on the back of the alternator. Looks like there's a lead that connects to the same place as the red wire that connects to the battery. Makes me wonder if its internally regulated and if so going through 2 regulators could be having an effect.
 

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The voltage off the battery without the car running is about 12v. With the car running it seems like there was less voltage about 11.8v.
OK, your charging system definitely isn't working. You might want to put a trickle charger on your battery.

I found the regulator and it looks to be original.
You mean the silver-colored box ahead of the battery, right?

Is there some way I can definitely check and make sure it's the regulator.
Yes. I described it in my previous post

Here's a picture of that black box on the back of the alternator. Looks like there's a lead that connects to the same place as the red wire that connects to the battery. Makes me wonder if its internally regulated and if so going through 2 regulators could be having an effect.
That black box is just a noise supression capacitor that reduces electrical noise so your radio doesn't buzz. Nothing to do with charging. Your alternator is the original type that came with '73 spiders. That three wire connector toward the bottom of the photo goes to the external regulator.
 

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I found 2 alternators that weren't charging because a wire to one of the diodes had broken at the solder joint. Resoldered them and carried on.
You can access that area by removing the 2 small bolts where the black plug attaches.
 
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