This article covers modifying the factory Fiero Performance Sound overhead unit so you can use it to adjust the volume of an aftermarket amplifier. This modification does not require doing anything to the amplifier itself, we will actually be adjusting the gain of the input to the amplifier. This way, you can replace your amplifier at any time and retain the volume control, also you don't have to worry about damaging or voiding the warranty on your amp

Here's what you need:

1. Fiero Performance Sound overhead console.

2. If using a deck without RCA jacks on it, e.g. a Factory headunit, grab a PAC LC2 High-Level converter.

3. If using a deck with RCA jacks, you should be able to use the PAC LC1 remote bass knob.

4. With the PAC LC2 You will need two small 50kohm slide resistors, here is what I used: Slide Potentiometers from Mouser Electronics  I do not have a PAC LC1 and am not certain if the resistor value is the same. You may want to purchase and disassemble one before finding the slide resistors.