1995 Ford Windstar alternator

In what way do they self-destruct? Does your generator have a rectangular plug on the side with two large black wires with orange stripes?

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Do you mean they simply don't work when installed, I hope? There really isn't anything in the vehicle that can destroy a generator, and by their very nature, they are self-regulating as far as current is concerned. They simply will not produce significantly more current than they are designed for.

First, does the battery light turn on as soon as you turn on the ignition switch? If so, that circuit is ok. It is the "turn-on" signal for the voltage regulator. You should also find around 2.0 volts on the green wire in the regulator plug when the light is on. Once the system is working, there will be near full battery voltage on that wire and that voltage will turn the light off.

Next, there must be full battery voltage on the yellow wire all the time. That is the main power source for the regulator and it is the wire the regulator uses to sense system voltage. If that voltage is missing, look for a blown 15 amp fuse.

There must also be full battery voltage on that fat black / orange wire all the time. If that one is missing, look for a blown very large bolted-in fuse. It could have been blown by the previous generator but more likely that wire touched ground and arced, especially if you didn't disconnect the battery while doing the replacement.

You won't find any voltage on the white wire at first, but when the generator is working, there will be near half of full battery voltage on that wire. It's that voltage that tells the regulator to raise the voltage on the green wire to turn the light off.

There are two ways to tell if the system is working. Look for around 6 volts on the white wire, or measure battery voltage while the engine is running. The voltage must be between 13.75 and 14.75 volts. Besides identifying a no-charge condition, the regulator will also turn the warning light on in the event of an over-charge condition.

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Did you measure the voltage on the yellow wire? You should not be disconnecting the output wire when the engine is running. The battery is a key part of regulating system voltage. 35 volts will exceed the reverse limits of the generator's internal diodes and one of them can short. That will lead to overheating of the other ones. As a general rule of thumb, when one diode is shorted, you will only be able to get very nearly one third of the generator's rated capacity. A 90 amp generator will only produce 30 amps which is sufficient for most driving conditions, but there will be excessive ripple that can interfere with some computers on the vehicle.

If you are getting no output at all when the units fail, look at the regulator on the back of one of them. You will see it is held on with four screws in a rectangular pattern, and there are two additional screws in the middle. One of them says "ground here to test". The other one might have a round gray plastic cap over it. Pop that cap off to take a voltage measurement there, or, it will be the same voltage as on that yellow wire.

When the generator is not working, ground that test point while the engine is running and you're measuring battery voltage or watching the head lights. The voltage should go up. If it does, all of the wiring is ok and the regulator is not turning on. If the voltage does not go up, measure the voltage on that point and on the yellow wire or screw that had the cap.

Just so I'm clear and don't overlook something, also measure the voltage on the fat black / orange wire while the engine is running.

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