Hello,
I was spring-cleaning my amplifier, disconnected the speakers,
cleaned the posts. While I was at it, I pulled open the fuse housing,
just above the power connector. A part from a strange-looking device
that actually holds the fuse, just above it there is a
plastic block which (I since found out) can go in either of four
ways. Here's a rough hand drawing of what it looks like:
http://home.comcast.net/~davehassan/block.JPG
The middle grey is the plastic block, while the outer green
is the metal conductor.

In the housing, behind this block are 6 pins, and either all,
or a certain combination of these pins will be connected,
depending on which way this block is inserted.

The problem is, I didn't mark the original orientation, and I'm
uncertain which way it goes!

I opened that amplifiers case and there seems to be a wire on each of
the 6 pin connectors. That seems to imply that the orientation of the
block is the bottom in (from my drawing) because that would affect all
6 pins.

If anybody knows or would check for me, I'd much appreciate it -
Dave