Sounds like you have 2 sources grounded. With a ground effecting the doorlocks or should I say 79-00 this can be bad! We would use a 200 Watt light bulb on a utility cord. Cut the plug end off and pull back wiring. Strip the White/Black and ground one end. Touch other end to (79,00,311,312,511,512). If 79 to ground lights the bulb your 00 source has a ground! You use a light bulb to verify it can carry current and is not induced! Also if you put your light bulb on 79 and it lights very faintly, start at the top of the controller picking up each relay momentarily. If the light gets brillant look for the contact on that relay causing it...Hopefully the mechanics have keep the power supplies seperated over the years and used the correct wiring colors for sources. Or you could be in for some FUN!