What was the 2 wire carrying? Video and 12 volt + ??
If the 4 wire plug is on the camera, maybe you could do without audio, run a separate wire from the 4 connector plug ground to chassis ground for the ground connection, and let the 2 wires carry video and 12 volt positive.
Of course, I've never tried this but I think it will work.
Fred
Fred & Vicki
St. Augustine, Florida