how do I reprogram a wired keypad for a garage door opener?
I have the same keypad outside the garage and a panel with large rectangular pushbutton inside. The Keypad is wired to the indoor panel and the panel is wired in turn to the opener. Have had it for 25 years since it came with a 1994 Craftsman opener. When the battery dies the code is lost and needs to be reset.

Make sure you have a fresh battery! There should be no need to disconnect the battery or unplug the opener. In fact, if you unplug the battery the circuit board in the panel has no power and cannot be programmed. What is being programmed is the circuit board in that panel NOT the opener as is done with wireless remotes for your cars or wireless keypads. The reason to unplug the opener is probably a safety concern. It is very easy while working with the panel to accidentally push the large button on the panel and operate the door opener! The door might strike you or someone else.

To program the following is the easy procedure Just open the small rectangular plastic plate on the panel where the battery is located, move switch to "program". Enter desired 4 digit code on the keypad. Move switch back to "operate". Test by entering the code.

Note: while the opener is working you can touch any key on the keypad to stop/reverse it. When the door closes you can re-open it while the light is still on in the keypad by pressing any key. Once the light goes out you must enter the 4 digit code again.