Hi there.

First off, my native language is Dutch so bear with me on the following:

I owned 3 Navigators, all 2003 models and all three of them with the well known electronic module troubles. I.e. running boards failing, power lift gate not opening, 3rd row seats inoperative, odd dome light behavior and so on.
This weekend i took the time to find a way to not cut wires or opening up wire looms at the start of the process but to get the picture straight on how to fix this before opening my toolbox.
To be clear, i have never had a failing module at the end, just symptoms that would suggest it. The dealership will tell you otherwise!)

This fix is easy but you must avoid cutting open wire looms if not really neccessary.
I started with the FSM in hand and checked similarities in the wiring to the different modules. Two important things as a result. An always-hot 12V wire (Red/White) and an UBP wire (Violet) through which communication between modules is sent.
First thing to do: check the 12V wire RD/WHT on an effected module because that's an easy one. There will be power or there won't be power. For example, i openen the left hand housing enclosure in the trunk (just lift the top) to get to the Lift Gate Module (this one takes care of the running boards and the power lift gate). Unhook the biggest connector and find pin 2 with the RD/WHT wire. Use a simple 12V light bulb tool. No 12 volts? Then you're home before dinner with a fixed car! There's only one splice that feeds all these modules. It is located inside the wire loom under the passenger side front sill plate, just in the middle (FSM indicates it is under the B-pillar). Remove the protecting metal plate/strip on top and carefully open up the wire loom. Find the RD/WHT wire splice, usually in the lower part of the bundle. Usually two wires incoming from the front and one or two outgoing to the rear. Cut open the plastic shrinktube and you'll see a corroded connection that can be in a so bad condition that it will fall apart the moment you open it up.
Cut, clean, reconnect and tape it in. It's just a 12V wire so extend it if you need to. To prevent it from happening again, pull the wire to the top of the wire loom so it won't get wet again.

Note 1: If you indeed did have 12V power on the module it will probably be the VT (Violet or purple) wire. It has the same problems but under the drivers side front sill plate. There's noting to measure there on the UBP bus but the cause & fix are the same.
Note 2: if, after this fix, your AdvTrack module keeps giving an error it is not broken, just confused! You'll have to use a diagnostic tool to reconfigure it. Only thing to do with the diagnostic unit attached is turning the the steering wheel to both stop points.

Time: 1 hour. Materials used: tape, crimp connectors or soldering. If i were living in the US, i would start a business with this :-)

 

Like they say, always check the basics before replacing parts. You got it!!! Just like a weak battery can throw off the modules as well. Nice job and thanks for the info!!!