I want to thank the three of you for your responses, as well as the generous offers to install the switch for free. Unfortunately, I am in New York. As for speaking to a Hafler technician, I did contact Hafler and was told that whatever info they have available, is on their website, however, a service manual for the 9130 is not available. As for speaking to a technician, I was told that without a specific working knowledge of the amp in question, they would not comment on how to install the switch. Would it be possible for one of you to send me simple written instructions or advise if I am on the right track. My perception is that the switch simply plugs in to an internal socket that is hidden by the front face plate. But not knowing for sure that removing the face plate will gain me access is why I did not proceed on my own.