Trev 29 has it right. I just went through this on my daughter's 240. The locks really acted crazy. Sometimes they would work, sometimes not. Sometimes they would lock and unlock while driving. The problem was in the switch connected to the locking button on the driver's door.

If you want to just get rid of all electric locking, take off the door panel and look for a three pin connector which will be stuck to the door metal, using a black tar stuff, near the rear of the door. This is the connector for the dual lock switch. Disconnect this connector and all electric locks are disabled. However, you'll find that all the doors except the driver's door will be pretty stiff when unlocked with the key. This is because you are having to move the lock motor at the same time. (Yes, there are small motors which operate each lock unlike solenoids as I had thought. I'm always learning.)

I disconnected the electric locks as described then went to a pick-and-pull salvage to find a replacement lock. I got one for $10. Be sure to find one which has good insulation on the wires. I tested the lock with an ohmmeter to ge sure it worked. The lock is actually double. There is a switch which connects to the push button and a second switch which wraps around the key lock. They are not hard to get out and replace. If you take one out at a salvage yard, study how it all goes together.