Quoted from LTG:Stern used to ship a harness with for 110V bill validators. Runs from up front to power supply in the rear. I don't know if they include it anymore or if it's available from them.
Quoted from DugFreez:I have also heard the 110v power extension cable that runs from the back box to the coin door can be requested (and is free) from your Stern distributor. The part number is: 036-5700-10
It seemed the early SPIKE 2 games all had them included and somewhere after Star Wars they stopped.
https://pinside.com/pinball/forum/topic/stern-nib-w-no-dbv-power-cable