To unlock a pannier that has lost it's lock but still has the backing plate in place:
Check the hole where the missing lock belongs. If the metal backing plate is still in position you may be lucky enough to be able to open/unlock the pannier by jumping to step 4 below. If not, follow the following steps:
To unlock a pannier that has lost it's lock and backing plate and/or remove it from the bike:
1. remove base of pannier (8 Phillips head screws)
2. retrieve metal backing plate, two screws and 1 rubber cover from inside pannier. They should drop out when you remove the base.
3. place the metal backing plate back where it belongs - check orientation (important) by looking at the positioning of the plate in the other pannier.
4. use a pair of needle-nose pliers inserted into the two screw holes on the backing plate and turn clockwise to unlock pannier lid at the same time pressing down on the pannier lid at the lock end. Turn anti-clockwise to unlock from the pannier rack so that the pannier can be removed from the bike
5. when installing the new lock check the orientation of the backing plate (looking at the backing plate on the 'good' pannier) and apply Loctite to the screw threads