1998 GMC Jimmy

If you are talking about eh where the key goes on the outside of the door you have to take the door panels off and take the spring clip off that holds the door lock in. Disconnect the linkage if there is any and there may be a screw or e-clip holding a piece on that must be transfered to the new lock. Or you can take the truck to a locksmith and they can make a new key for you without all that work.