If the central locking system relays are the problem, then yes, they are the commonly found cube-shaped relays. The ones to use are the five-prong, DPDT type. Don't know the power rating, you'll need to look on the covers.

There are two and they are located on the relay-mounting rail below the center dash air vents and just forward of the coin tray. Not hard to get at.

A hung up relay drains the battery by continuing to feed power to the lock actuator magnet even though the lock has moved. Usually the locked position, as that's where one leaves it when shutting down for the overnight.

However, the actuators are subject to damage from aged hardened lubricant and just plain rust. BTDT

If you pull up on the driver's knob while pulling up on the knob on the passenger door, is there any movement quickly, and complete movement later?

A question for you - was something wrong with the central locking system that came stock with the car? Is your addition a remote locking?

Good Luck,

Bob

:>)