What do i do about it?
Go ask for the key and take the lock off !! 
Why would soneone lock it? 
To stop someone hooking up to it an driving off if its on a bay being loaded. Or to stop it being nicked if left somewhere.
Its a Suzie lock, once you have permission, get the key and take it off and then you can connect the red line to the trailer…
ah and remember to give the lock and key back to the office as it will save some embarrassment later 
Cheers
Tooz:
Go ask for the key and take the lock off !!
DOH…[emoji56]
Hmmm as said it’s an air line lock, to stop someone connecting up to the trailer and driving off with it. Mostly used for VOR trailers at most places or sometimes locked off whilst on a bay.
Asking the right questions is always important.