The early 90s keyads were purely lock/unlock of doors with just basic horn honk if door opened. Inserting the key and turning the ignition was one way to disable the alarm (or just break the ignition cylinder and turn). My grandfathers 89 thunderbird SuperCoupe had that system. No ignition protection like the newer style PATS.He wants the numbers on the door you use to unlock it that style,I have seen it on lincoln towncars of the same age so it could work but never tried doing that.The easiest thing would be a aftermarket alarm system vs trying to make a 20 something old ford system work.My security system is a shotgun and a big dog.
Generally, the intention is to make it inconvenient for the casual thief/joyrider so he/she/it gets frustrated and moves to something else. Deter opportunistic theft. Not intended to stop someone who has specifically targeted your car.Seems like a lot of trouble for not much reward. Just hide a cutoff switch somewhere that won't send power to the computer/fuel pump whichever you prefer.
If anyone wants your truck though, they will just tow it away regardless of what system you have on there.
Two 12v wires to the computer. Keep Alive, and Run. You kill the power to the Run wire/relay, and leave the Keep Alive wire alone, and it wont have to relearn anything. Same as a memory wire on a radio.I don't like the idea of killing power to the computer, as then has to re-learn.