Assuming this is the only opening, big assumption, buy a plastic bee escape, the small white ones that go in the hole of an inner cover, get a board large enough to cover this hole, cut a one inch hole in the area of the board where the bee entrance and staple the bee escape over that hole. Use duct tape to attach the board over the entrance, bee sure to cut notches for the cables and tape around them to seal it real well. If you use an election type, plastic corrugated board as the board, you can cut it with a knife on site.
Good luck. The only problem that I see with this trap out will bee how many ways can the bees access this area.
Jim