OK--he is posting in the Alpine forum, so --oops.....though it would be nice if you included the year and model of your Alpine in the body of your post or added it to your sig blk. On most Alpines, the are a couple of water-proof fuse holders on the aft bulkhead of the area ahead of the front wheel well--same area as the hydro- boost is located. These holders contain both fuses and one-way diodes that control the HB. Some newer coaches [post-Vansco] are designed to have the HB work only when ignition switch is on -- assume since yours "stopped work", something has changed from expected/normal operation?.
2003 40' MDTS
Garden Ridge, Texas