Mike,
All I have is a hand-drawn schematic and layout that I did for my former 1970 Sonic 1 (200S) that has moved on to a guy in Canada. It is on large paper so it would be hard to scan....but I can tell you how it should be connected to get the lighting working on the power switch. That said, why use the original power switch? If they go bad, you can't find any easily. If you aren't going to use an original style lighted power switch, then it simplifies the wiring.
The proper way to wire a 3 wire power cord is that green should go to a chassis ground that is separate from any other ground within an inch or so of the power plug or cord. It should also be connected with a little slack so that the last thing connected in case of the power plug being pulled out is the chassis ground connection. Having it's own bolt that is attached with a nylock or better a keps locking nut is very important for safety reasons. You don't want to connect it to a transformer bolt as what happens if someone works on it and doesn't properly attach things again.
The "black" wire, otherwise known as the hot wire should go from the power plug to the fuse, then to the power switch, and then to one side of the primary winding on the power transformer. The "white" wire, otherwise known as the neutral wire should connect directly to the other side of the primary winding on the power transformer. This connection needs to be secure so you need to install a terminal strip and connect these two wires to one of the terminals rather than trying to connect them together directly.
The original Sunn power switch has a fourth connection that is for the light. The light connects across the primary, but is switched with the power switch. The white wire goes to the power switch and to one side of the light. The black wire goes to the fuse and the other side of the light. The most likely reason the light doesn't work when the power connection is modified is because it loses one of it's connections to either the white or the black wire. I would have to mess around with my 2000S to be sure, but I don't have time right now. I do plan to overhaul the amp at some point and go to a 3 wire power cord and will need to modify this area of the amp, but its a ways off for me right now. You could wire yours up the way I described immediately above and the amp would work and be safe. It just isn't as safe as the first way I mentioned. An even safer way is to wire it like Marshalls and put a fuse and switch in line with each connection. This uses a DPST switch instead of a SPST switch.
If I was building a Sunn clone, I wouldn't be so concerned about the cosmetics that I was using the same identical switches....they are very hard to find and you can only get them used and they weren't all that great of a switch anyway. I tend to use a lot of Carling switches like Fenders use. These aren't lighted though, but you can always use a seperate pilot lite like Fenders or the neon ones like Marshalls. You could also use a lighted Marshall power switch too. These aren't that hard to wire up and can be done safely, and are readily available. I would also use an IEC power connector instead of a hard-wired AC cord. You can even get these with the fuse incorporated into it and they are safer and easier to wire up and use as any standard cord will fit. There are a number of other changes that could be made but these are the basics that I would start with.
Does that help?
Greg
