[Rick Parker]

In your diagram it appears that the "labeling" of the respective circuits for the amp gauge is reversed from what it should be. The battery pole should be attached to wire 27 and accessory pole to the switch. Also the arrows on some of your circuits should be reversed to indicate correct current flow. ALL of the current is originating at the solenoid battery connection, goes through the AMP gauge (to be measured) and then to the fuse block and ignition switch to be distributed. If you have solid 12 volts at the back of both poles on the amp gauge and at the fuse panel where 41 attaches and at 24 then I would say your switch is bad. If you only have 12 volts at one side of the AMP gauge then you have a bad gauge. You can have the alternator checked at Orieleys or Kragens for free. I would appear that based on your diagram that all current for the alternator goes through the switch.
Keep us posted. This type of experience really helps you (the owner) understand how electricity is distributed throuout your vehicle. It is very satisfying when you are able to finally anylize and solve the problem.
Let us know what you find.

Rick