Bonnet cables fitted to TRs have no reason to break if they are regularly inspected and lubricated. If the cable does break some serious 'fiddling' will need to be done to release the mechanism. Be aware that bending up the corner of the bonnet and trying to pull the catch with a bent wire coat hanger is not only expensive on bonnets but likely to cause an electrical fire if the battery terminals get shorted out. If in doubt about the quality or operation of your bonnet release cable get it fixed, or install an emergency bonnet release kit as a back-up (603468-9EBR or 630573EBR).