Username is vehicle in question with a /6, Ive done radio swaps, swapped alternators, grounded the radio, grounded everything else, even installed a noise suppressor on the Alt. Power line and then swapped it to the radio power line and I still get interference that varys with engine speed. If I disconnect the Alt power line the noise stops, What can be causing this and what do I do to make it stop? Im at my wits end with it!!!

Sounds like you have a leaking diode on the alternator rectifier circuit. Do you know that the second alternator you installed was operating properly or could it be plagued with a problem the same as the first one? RMDV

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Carl Zeamer. an old guy, please be gentle.