Review on Metra 70-5603 Amplifier Integration Harness: Enhanced Compatibility with Ford Vehicle Models by Brandon Gaines

Not for 1997 Lincoln Mark VIII with JBL Premium Sound. I've spent a lot of time taking apart the wiring and trying to get it to work. I have a complete wiring diagram for this car. If you only used the signal cable (+) (center electrode), it carries the sound to the amplifier. But there is a lot of signal noise. The outer shield connects to the (-) speaker wire in the wire harness, grounding the signal. I believe that the fact that the secondary amplifier is intended for speaker level inputs makes it essentially impossible to solve this problem with RCA preamp wiring. The outer shield wire must be routed back to the amplifier itself somehow. Grounding not working. So I have to say it's just completely useless and I've tried every possible solution. Follow the speaker level inputs for the standard amplifier as provided from the factory. Otherwise, it's time for aftermarket amps, and then you can use the head unit's preamp outputs.