Yeah, didn’t want to tamper with it as I know the US build ones are definitely open - for plugging in devices, soldering irons, test units etc.....
The Mod couple Bat Signal relay device was designed to plug in here and the mod connection was USA 3 pin - this service outlet would have to be converted to 220 volt UK supply so maybe understand why it’s sealed off, maybe Stern didn’t fully complete the service supply to work in UK.
I got around it by purchasing a step down voltage converter and bypassed the Pin machine altogether and powering the projector from the AC which is the safer option.