You're going to have to find the module if the code stickers aren't in the usual places.
I'm not too sure where the module or the code stickers are located in the 1989. I've heard some are in the trunk as pictured in the attached link, some are behind the glovebox compartment, and mine (1996) is inside the drivers door.
The code sticker should be on the module too, but in case it's not, you can open the module and determine the code by
reading the configuration of the resistors.
bdklein put together a very nice page on changing you factory code, which details how the codes are set at the factory.
check here for module reprogramming:
http://webpages.cwia.com/~bdklein/sho.htm
check here for general programming when code is known:
http://www.lincolnsonline.com/article13.html