Your situation seems weird, if an Openreach tech had brought the ONT with them to install FTTP when the plot was called off by the developer ( but before the purchaser moves in ) , why leave it in the box and not fit it in the normal way , if the development was DSI ( developer self install ) that’s where Openreach make an extra payment to the developer , and they fit the ONT themselves, it’s usually the electrician, who probably also ran the internal optical cable from the location of the ONT inside the house to the location of the CSP on the external wall , so why didn’t the developers ‘sparky’ fit the ONT ? , having said that even on DSI , Openreach still visit to splice the fibre in the CSP and authenticate the the ONT , so the ONT still being in the box suggests a developer that hasn’t a clue.
I know of situations where , the developer basically hands over the plot , before telling Openreach , or they release the plot to the purchaser, before they have provided the Openreach ducts and boxes necessary for the FTTP network cables , and by the time they complete this work , every time Openreach visit , there is no access and obviously they developer no longer has the keys
In these situations Openreach leave a card , asking for the occupant to arrange an appointment ( directly with OR because at this stage there is no ISP involved ) and that request goes unanswered, sometimes be because they have decided they never intend to use Openreach, but should they rent , or sell , it screws up any future occupants, this can also happen if the plot is bought ‘off plan’ and the purchaser has no intention of ever living in it , but intends rents it out and basically never actually visits the property and the letting agent they use gets the keys from the developer .
Anyway , you could connect the SC/APC plug into the appropriate socket on the ONT and power it up , but it won’t be authenticated, so even if you do it connected correctly and don’t damage either the cable or ONT , chances are the PON light will flash ( signifying no authentication ) or the LOS ( loss of signal ) will be lit , signifying there is no light being detected, so your fibre isn’t spliced through to the splitter, so either way it won’t speed anything up , so it’s wise to not touch it at all .
In the situation I describe ( where the Openreach newsites tech can not get access ) they arrange to get the address inhibited from making an order ( because the kit hasn’t been provided and authenticated as a normal newsites address) but it should be possible to resurrect the address on OR systems , but it will ( unlike most new builds with FTTP from the outset ) need a ‘service delivery’ visit , and the ISP ( BT in your case ) to join the dots.
