12 v (DC) runs between 1 -> 2, 1 -> 3, 1 -> 4. I put the pos on 1 and then put the neg on 2, 3 and 4 pressing each button at each connection. All of them react in some way except listen.
For talk
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1 -> 2 - is drops to 8.5ish
1 -> 3 - is drops to 0
1 -> 4 - is drops to 8.5ish
2 -> 3 -...