Mercedes e320 with a shit sony head unit. I put the positive to the end of one of the RCAs and grounded the negative side. Is that the wrong way to do it. That method seemed to work for the power and remote cable.

No, connect the ground to the outer lugs of the connector and the positive lead to the center. This is AC current, not DC with the vehicle as a ground.

And what is the model number on the Sony HU? I think some of those you have to go into the menu while it is off, with the vehicle on in order to turn on/off the subs.

Edited July 12, 201015 yr by sandt38

It is a CDX-gt240. So let me just be sure I tested the RCAs right here is what I did. I turned on the car and turned the volume up to a decently high level. I then turned the dial on the multimeter to AC and the closest setting to 5 was 10 so I put it there. Once all this was accomplished I put the tip of the red tester thingy-ma-bob onto the little post that sticks out of the center and the black one on the outer metal ring type thing. Is that right because in both mine and my friends car we got nothing and to the best of my knowledge his RCAs should be working. The amp and all that has been taken out for a while but we checked and they were plugged in so what gives?