You can only use the electronic flash on the Speed Graphic when the shutter is completely open. This is the case only when you use the T position. On every other speed there is a slith with various width running over the film plane. When using flash bulbs, the bulbs burn sufficiently long to be used on 1/1000 of a second. You can attach the cable release directly to the body release on the Speed Graphic. Make sure the body release is set to release the curtain, not the between the lens shutter. There is a switch on the shutter panel on the body, and it should thus be set to Back. Good luck!