Has someone just removed the top box & fitted a flat panal with a rack?
If so should be an easy conversion back to standard, if you look on ebay there is a top box & all fittings for sale near you for £300 if thats your intention.
There was a company in the US that made those kits and the original wiring is probably under the top panel. I believe the company was MBL Innovations that offered the kit. You may want to contact them. https://mblinnovations.com