on a convertable the amp is behind the rear seats on the drivers side maybe in urs it will be around by drivers rear quarter panel. the converter plug will be rca type plugs (low input) and you will need a stereo with front and rear audio outputs there will be a remote wire to activate the amps built into the converter. this is so you still use the original amp which I think is alpine.try
www.autoleads.co.uk the amp on a cabriolet is about 12in square so you can miss it if its the same as urs!