Aftermarket radio not outputting audio
 

I have a 1997 se sedan and I recently bought an aftermarket radio, Sony MEX-GS820BT, and the unit turns on but outputs no audio. To the best of my knowledge, I believe the wiring harnesses are correctly wired up and only one pin differs between the new headunit and the car's OEM wiring; the 'amp on' pin wire is missing from both the Nissan-ISO and ISO-Sony wiring harnesses. The speakers do not even turn on, leading me to believe that there is a factory amp somewhere in the car no longer being turned on. However, I've replaced the rear and front speakers and have never seen an amp anywhere near them like the factory one would usually be found, nor can I find an amp anywhere else in the car. If anyone can help me diagnose the problem before I return the unit I would be grateful. Thanks in advance.

Did you replace a Bose or non-Bose radio? The Bose radio has an amplifier on each of the speakers. There is no amplifier in the non-Bose.

Did you use a Metra (or other brand) wire adaptor? If so, what is the adaptors part number? Please don't tell me that you spliced into the Nissan wire harness.

Nah nah nah, tried as hard as possible to avoid touching the nissan harness. The stock unit was a 2-din clarion cassette and radio and I've actually just located the amp (FYI it is in the boot bolted to the back seat located on the passenger side behind the material boot liner).
https://cimg3.ibsrv.net/gimg/maxima....848372fc82.jpg

That is an aftermarket amp. Nissan did not use one - at least in the North American cars.

If you need an amplifier on wire, tap into the blue/white stripe wire in the Sony wires that is labeled REM OUT in the Sony installation guide.

This is an Australian import so I'm not sure what the factory options are but that amp is definately factory.