When you say it will not "click in place", is the plastic tab not going down into the groove, meaning does it not bend down or is the edge of the tab/arm too big to fit into the groove? If you can look at it closely, you need to see if the arm is just sitting on top of the groove; it is possible that the arm is too fat and/or the groove on your speedo is too narrow. If either is the case, you can carefully shave down the end of the arm to get it to fit in there.