Dealer had my car for 3 months to replace a door lock still not fixed.

[AndrewAMG]

So the dealer had my brothers car for 3 months pull most of it apart... never fixed. I told him to not take it there and let me do it but they learned the hard way... Its never easy to go back in after someone else worked on it and didn't fix it to troubleshoot this has been my life for the last couple days.

This all started a year ago with the rear drivers door lock not working.
The dealer replaced the door lock and still didnt work.
The pulled half the car apart and found water in the floor under the drivers seat.
The harness connectors had been submerged and corrode they cleaned what they could and spliced what they couldn't. They never did get the back door working. They also bricked the car and gave it back after they unbricked it with more problems then when we dropped it off.

This was after paying thousands of dollars to accomplish nothing.

They said water was getting in but didn't find out where. Needless to say its two common problems sunroof gasket shrink and the sunroof drain fall off the connector to the outside. I literally found the issue in under 5 min.

I had to pull the evaporator out which caused the dash to come out so I corrected the drain problems. We have replaced the gasket and there is no more water in the floor. PS you can get to the drivers drain without taking the dash out. Never tried to get at the passenger one.

This was all under the guise that it would be covered under warranty or else he wouldn't have stepped foot in a dealership EVER !

I have come to the conclusion that the wiring is still compromised. I want to continuity test the wiring inside going to the rear driver door yesterday I took it all apart follow the harness back but it disappears into the main harness never to be seen again. I don't really want to unwrap the main harness.

This is the symptoms the door is completely dead other then 12v at the window motor computer. None of the buttons work, the lock and window do nothing.
I pulled the window motor and computer in one and moved it to the other rear working door it works the motor so I'm thinking there is no issue with the motor or the computer in the door.
I opened the wiring loom that goes from the body to the plug in the door nothing visually looks broken or frayed but that doesn't mean much.
I also saw that since we are using the front drivers switch to try and activate this and that somehow that might be linked and the drivers door loom gets opened 50-100% more then the back door inspected that wiring that goes from the body to the door and it visually looks good.

I'm still thinking that one of the wiring plugs in the floor might still be the issue even though its been dry for months and there is no new corrosion and to my knowledge everything seems to be connected correctly.

There are very few wires going between the body and rear door maybe 10-12 and the two heavy power wires seem to be good.

I also checked the fuses under the glove box they are fine for both doors.

We would really like to get this resolved without replacing the entire car harness.

The code is DDM U134787