Guitar amp
Replacement on/off switch
Dpst rocker switch
Which wire to which pole

There should be 4 terminals on the DPST switch. If this is indeed a toggle and not a slide then pretend the handle extends.

Code:

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1a    1b

2b    2b

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Between 1a and 2b is 1 pole (switch)

And between 1b and 2b is another pole (independent switch)