The car has been running great. One day when I turned the key to start the car, I heard a buzzing whistling noise from under the hood. Upon investigation the noise came from a black box on the driver side close to the front of the car. There are two connection boxes hooked to it. I would greatly appreciate any help I can get to get this car running again. Thanks.

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1980 - 300D
1984 - Mazda B2200 Diesel