I am installing an F700 in an 04 Escalade. I have BOSE and ONSTAR so I am using the GMOS-04. My front two speakers are working great but when I plug my rear speaker outputs from the HU to the inputs of the GMOS-04, it kills all of the audio. If I plug the RCA connectors together with just the center pins touching, i get audio. As soon as the grounds touch all audio is killed. Does anyone know what may cause this problem? Thanks in Advance

bad gmos04 - yes it can happen, gmos 01 and 4 oth have had this issue in the past...