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I've gone the opposite direction. You have to also swap bumper lights as the signals are in the bumper and reverse in the upper lights, but it's a simple matter of matching white colors when you swap the plugs.
I've seen plenty of 03-04 D2's converted to 99-02 setups. I haven't done it myself as I only have 1 04 and it's rear lights are actually decent (drilled holes in the back to let any water drain so it keeps it looking new vs turning black).
Just spend a few hours working on this tail light situation. The conclusion I have come to, you can't run the early model lights in a 2003-2004 without a separate turn signal lamp. The reason is, the older style doesn't have a multi-function bulb. So, if your marker lights are on, they will override the turn signal. Okay, how about the brake light? Same thing. If the brake light is on, it will override the turn signal. The late model D2 has separate outputs for brake, signal and running lamp so you can't combine any of them.
I'm guessing the older D2's had turn signals in the bumper? Not sure. But, since I have a Greg Davis rear bumper, I have no lights anyway. I'm going to find some aftermarket turn signal lights and mount them to my rear bumper, then the early model lights will work for running lights and brake lights with turn signals in the bumper.
Okay, I'm not sure why this didn't occur to me, but it should have. I ended up using an amber bulb in the reverse light and wired the turn signal to that (saw that in a forum somewhere). It worked great.
So, to answer my own question: yes, you can use early model tail lights on an '03-04. You have to wire it up and both sides are completely different. The wire colors make zero sense and you'll have to experiment with what is what (twice), but it does work (eventually).
I think these tail lights look way better than the late model lights. And, I can't find replacement '03-04 lights anywhere even if I wanted a set new original style lights.
Here's the break down:
Main Light:
Top most 2 bulbs: Running lamps
Center large Bulb: Brake light
Bottom bulb (was reverse light): Turn signal (amber bulb)
Lower in-bumper lights: Reverse lights. I have a Greg Davis bumper so I had to add some aftermarket lights.