I need one wire for my Audi 90 and I can't buy a set. It the core wire.
are spark plug wires interchangeable with other years and models of the car. on 1991 Audi 90
Look at www.rockauto.com ,they usually have good images of parts, see if the part number crosses over to any other car.
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Your local parts store should have a breakdown of what is required for each wire in a set or take old one in and they can match.