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I put a Milano alternator in my spider. Everything was fine for several months. Now when I turn my key off the generator light comes on and stays on. When i disconnect the green wire coming from the fuse box to the alternator of coarse the light goes off. The battery is holding a charge and a constant voltage around 11.6. Does any one have any suggestions.

Thanks

Ryan
 

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ALT light

The alt light illuminates when there is a potential across the lamp.

Green wire doesn't directly come from the fuse panel. Power from the fuse panel -> to the instrument cluster -> to one side of the lamp. The other side of the lamp exits the instrument cluster (this is where it becomes a green wire) and connects to D+ on the alternator. D+ connects to one end of the rotor winding, the other end connects to ground.

Disconnecting the green wire from the alternator and having the lamp go out indicates that you have broken the circuit, duh.

Based on my 86 Spider:

The lamp normally goes out when you turn the key to off because the ignition switch disconnects power to terminal 15/54 which powers directly the ignition ECU, the + terminal of the coil, creates the hot side of fuses 6, 7, and 8.

If the ignition switch is not breaking power here, I would think the car would keep running.

Fuse 8 supplies power to power window relay, rear defogger relay, glove box light, instrument cluster. If you pull fuse 8, does the light go out? The 12v going to the cluster and Alt lamp is also the 12v supplied to the volt meter, oil pressure gauge and lamp. do any of these still stay on? Oil pressure gauge will go to zero but is low pressure lamp on? Voltmeter showing volts?

Verify fuses 6, 7, and 8 lose power when the key is off.

The alternator is not storing or creating volts when not turning so it is unlikely the lamp is lighting because the alternator side is enough greater volts than battery voltage to cause it to illuminate.

So the battery side of the lamp is getting voltage from someplace.

any other electrical work been done just before this?
 

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Simple test to determine if the problem may be a shorted diode or faulty regulator.

Disconnect battery.
Disconnect large wire from terminal B+ on the back of the alternator and insulate it from touching ground.
Hook up battery.

If the alt light is now off, the problem is in the alternator.
 
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