One of two possibilities:

1) You're not pushing hard enough. After the driver's door locks, when closed, push harder down on the button and see if the passenger door locks.

2) There's an intermittent break in the door wiring harness at the hinge, and unlikely as it seems to me, it makes contact when open but breaks the circuit when closed.

In any case if the passenger door power lock EVER works, you've got good fuses and good lock relays. The circuit basically works. There are 2 relays, and they perform "lock" and "unlock" for the whole car by switching either the blue or the yellow wire from 0V to +12V.

The rear door locks either are disconnected, at that 2-pin connector I mentioned, or their dooor hinge wiring is damaged, or, as occasionally happens the lock motors have gotten wet and rusted and are no good anymore. The motors are universal; they can be unscrewed from their brackets and unclipped from the rods and swapped, so if you find a good one in a parts car it can be used in any location.

In my cars, I've added a driver's door lock actuator so I have a power lock on the driver's side as well. This allows me to install a keyless-entry controller and lock and unlock the whole car with a click of a remote. It's a simple install but it does require you to get a passenger door lock linkage and a bit of extra wiring harness. I can give you more details if you are thinking about anything like this. First off, though, the factory power locks have to be working right.
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::: Rob Bareiss, New London CT ::: 92 244 ::: 90 745GL ::: 90 745T ::: 84 242DL ::: 90 745T Parts ::: Used to have : 86 244DL, 87 244DL, 91 244, 88 244GL, 88 744GLE, 82 245T, 86 244DL, 87 244DL, 88 245DL, 89 244DL!