t-belt covers and count the teeth between the CAM marks and the crank sprocket mark. It's a big pain in the ass to do - so I'd suggest making sure your timing test is being done accurately first. You've already started/run the car -- so it's not like you'll be causing any (more) damage to the engine if the t-belt setup is not right....
Why don't you try the light on another car - just to confirm it's working OK?