This Aquatica Switchboard Circuit is a replacement part or can be used to upgrade older housings. The board has four 2 position switches. When all the switches are in the upper position, it allows use of a TTL converter or housed TTL compatible flash that is attached to the main connector. When the switches are in the lower position (default), the main connector will work in manual flash mode only. The secondary connector is used to add a second manuel flash.