The instructions for the Breakaway are easy enough to find online, if the van was wired up for NSW it will have a purple wire for the breakaway monitor in tug, as NSW required one to be fitted in tug, other states didn't, NSW doesn't require it anymore ....if this is in the van plug then disconnect it and your problem may be solved........ the Breakaway should have just a 12v supply from tug to charge its battery but it may be getting power from the 12v van supply loom elsewhere....... the blue wire is your brake wire so that should be the only one on the #5 pin ....... a meter on this pin should only be active when the brake pedal is pushed or the button on the controller, if it stays alive when neither are operated then you will have to find where the power is coming from by simple disconnect of any other live wires... (pull pin on breakaway will activate the blue as well)
Take Note that wiring found in caravans may vary between fittings, do not assume RED is POS (+ve) and BLACK is NEG (-ve) , sometimes White can be NEG( -ve ) with BLACK POS (+ve) , so it pays to check the polarity of connections when testing circuits ..... brown will come into the equation as well at times, mostly lights though. 7 pin plugs are pretty standard the 12 pin can throw the odd curly colour so always test to confirm voltage and polarity, some equipment will not handle reverse polarity at all, don't assume it was wired correctly in the first place, you can even find a mod may have been done further down the line out of sight, the fuses in the fuse board may not match their labels either, you pull a fuse and the circuit you are working on is still live, test always to be sure.....