So I cannot say for certain whether the rear windows on my 2003 D2 have ever worked since I've owned it. I do know that no matter what I do, I can't get them to respond. So far:
- tested using both front and rear switches, and changed the front switches to known good units.
- tested with the cutoff switch on and off.
- changed window motor on one side for a known good unit.
- changed the cabin fusebox for a known good unit (the D2 electrical manual states that there is a rear window relay built into the fusebox).
- tested for voltage at the window motor (0v).
- tested for voltage at the window switch (0v).

The sunroofs on this truck also don't work, even though all components in that system seem good. I'm not concerned about those as they don't leak and I don't want to tempt fate, but is it possible that both the rear windows and the sunroofs have been deactivated in the BCU somehow?

 

Normal circuit tracing is what you need, go upstream from the switch till you find voltage.

Use the Rave. Also check the grounds. You should have voltage and ground at each switch.

If you do not have voltage at each switch there is an issue with either fuse 13 in the interior fusebox or the rear window relay. Check for voltage there.

If you don't have voltage there you have an issue in the engine compartment. If you are not familiar with circuit tracing I am sure there are probably pages or videos on the internet for instruction.

 

There can't be a problem with fuse 13, because the front windows also run through that and they work fine. Plus I replaced it just to be sure. I figure the issue has to either be a logic issue, or somewhere downstream of the circuits that are common to both the front and rear windows. I will try to do some more detailed tracing over the weekend, time allowing.

 

Have you checked both switches for rear window? The one on the rear door & the one you have for driver use,
once I had a problem on my 04 the rear left window stopped working because the switch on the door was bad , in my case that rear switch was the problem that it stopped working , I think somehow they are connected .
I replaced the door switch and it was fixed.

 

Yep, not a bad idea to check the rear door window switches.

 

I had rear window issues w/ my 00 Disco as well when I bought it.

Left rear wouldn't go up, right rear wouldn't do anything.

Swapped switches, etc... and turned out to be bad rear window switches in both cases. Not sure why but new switches fixed it. The switches are connected in a way to the front switches that a bad rear switch renders the windows erratic or inoperable.

 

Changed out both rear switches and the front switches for the rear windows. No improvement.

 

We can assume you checked the rear window inhibit switch too? Just asking the obvious, you probably did.

 

Second item on the list in y original post.
Also, that only affects the rear switches, not the front ones.

 

Fuses #13 sends power to the rear window lift relay (R3) in drivers compartment fuse box, #29 througg IDM. Pull relay, turn ignition to position 2, check for two hot sources in relay terminals, if you have two hot terminals, fuses are both good. So, that would lead us to the BCM, which l believe sends the ground signal that activates relay. If the fuse box is loose/hanging out, back probe the ground circuit of the relay with a ground wire you've made up. If the relay clicks and windows work...BCU may not be communicating with new IDM or BCM is bad. The manual says that if you swap out a new IDM (which you did, it's built into fuse box)... you must leave the key on for 5 minutes afterwards, so the BCM and IDM can communicate and get to know one another, turn key off...then turn back on.

lf fuse box is mounted, pull relay and just jumper terminal 30 and 87 of the relay. If windows and sunroof work...again...it's looking like it's a BCU issue.