The lever and lock that operate a bonnet are connected by a simple bonnet cable and, much like any other cable, it is prone to wear and tear. They are built to withstand heavy use but it is common for them to go slack, wear away or snap completely over time. Once you have found a replacement, the easiest way to fit it is to tape it to one end of the old cable and guide it through to the other end by pulling one way and pushing the other. If you pull the old cable out entirely first, it will be very difficult to find the same path for the new one to follow.