Music Man Amps

Hello,

I'll realize some maintenance operations on my second One Thirty (N/S 007686) :

I observe that the On/Off switch on the rear panel is different from my other One Thirty (N/S 006227) : This switch is a Kautt & Bux BN P1 250Vac 3(2)A / 250Vdc 3A.

In my opinion, it's a DPST (4 pins) but.:..

Pin #1 : 1 => fuse than primary PT / black with two yellow line wire
Pin #2 : 1 => AC network plug (phase) / brown wire
Pin #3 : 2 => primary PT / black wire
Pin #4 : 2 => AC network plug (neutral) / blue wire

Normally, a DPST (Double-Pole Single-Throw) switch turns two circuits on or off using only a single actuator.
With two poles and one throw for each pole, DPST switches have four terminals — two inputs and two outputs. These are essentially two SPST switches built together, affecting separate circuits but controlled by the same actuator...

I observe :

Switch Off =
Pin #1 connected to Pin #2 !
Pins #2, #3, and #4 disconnected
Switch On =
All four Pins connected.

I don't understand why. For me, Pin #2 and #4 are the inputs and Pin #3 and #4 are the outputs of this switch, so :

Switch Off =
All Pins disconnected, except perhaps pin #1 and #3 because primary PT winding assure connection ?

Switch On =
All four Pins connected.

Have you an idea ?

Thank's in advance !

Lionel