If they bypassed the ammeter it should not be showing anything. see if you can get some photos of the front and back of the ammeter. THERE is a possibility that someone did a VOLT meter swap?
Is the car stock or does it have added on electronics (fans, stereo etc)
Did your solder stop the high current charging? I would trace that down fast as that indicates either the VR is getting too little voltage and is increasing the charging to compensate OR there is a large load on the system