Hi, because this thread was very helpful I registered just to post the following, for future readers:
I have a Nord Pad but no Drum, so I wanted to adapt the Pad to trigger any drum module.
I can confirm the final two pins of the RJ45 are voltage and neutral. #8 is neutral, pin #7 is positive voltage.
The purpose of the voltage input (as in, electricity supplied BY the Nord Drum TO the Nord Pad) #7 is to amplify the signals from the drum pads. Inside the Pad there are two amplifier chips (Z974 see data sheet
https://www.ti.com/lit/ds/slos467h/slos467h.pdf). You don't necessarily need this voltage, as without a power supply the output from the pads will still come out from wires #1-6, as long as you wire up all the triggers to the shared neutral #8. If your drum module is able to respond to the low voltage output without amplification you'll be fine without the amplifier chips and won't need to wire up #7.
If you do need amplification, you probably won't need much voltage. The Z974 chips are rated 2.7V - 15V for their input voltage but I found I was able to get a good signal boost just from a minimal voltage. I found the chips heat up with a higher voltage so it'd be best to use the minimum voltage you need to trigger your module adequately. When I wire everything up properly I will try installing two AAA batteries (3V) but you could also power by USB (5V).
I don't have access to a Nord Drum 2 so I don't know what voltage it outputs as standard.
The Nord Drum 2 is hard to find, even second-hand, but I was able to buy a Nord Pad brand new on clearance. So if you're willing to do a basic bit of electronics to wire it up, the Nord Pad is still an attractive and probably cheap option.