Hafler 9130 power amp

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. 

I want to thank everyone who weighed in to help, especially Rodman99999. Your input is most appreciated!!!

Thanks for the fantastic pics Mofimadness.  I printed them out and will perform the install today. Both you and rodman99999 are the best!!!  

I just removed the top cover of the amp and immediately noticed that the two white wires that attach to the left and right front panel output controls in mofi's second pix are totally missing. Does this mean that I am not getting full output?  

So the gain controls being bypassed is not only a good thing, but a primary tweak. Knowledge is power. Once again, THANK YOU! BTW, I completed the switch replacement in less than 5 minutes thanks to you guys and the amp is back in service. Have a great weekend.