Hi everyone. Update on the situation, I got my front door pocket lights and footwell ambient lights working too. My wiring would probably give most Tesla fans a heart attack to witness, but lets just say there was a lot of t-taps, butt connectors, and messy electrical tape work going on. I'm by no means an electrician, and different model years and options may have different wire layouts, so proceed with this mod at your own risk. I'm not an expert, but I've done wiring mods for sound system, engine swaps, and interior option additions on my previous cars (replacing manual seats with power, etc). Some pics of the results (sorry for my bad photo skills):
View attachment 524949
View attachment 524950
View attachment 524951
First step is finding switched 12v power. I used the common VC_left point, which is found on the drivers kick panel. There are several videos on that, so I'll leave that to you. Don't do what I did initially, which was to T-tap into the blower motor harness. It worked, but only with the climate control on, haha. Find the trailer wire or a better source of switched 12v.
I then removed the trim panels from the passenger kick area as well. Wiring up the footwell lights is self explanatory. Cut the positive wires to the lights and wire in your new wires going to the power source wire from VC_left. Driver side footwell positive light is red, the passenger one is a light grey. Black is the ground, leave that alone. I didn't bother taking pictures of this process, as it's the easiest part of the job.
Now for some fun, want to feel like you're defusing a bomb in your $60,000 car? Perfect, lets play roulette. Just kidding, I got in the zone one night and poured over the wiring diagrams to the 2019 Model 3. I identified the pigtail connectors for the door wires. Good news is the front door wires are super easy to access. Bad news is the rear door harness is in the worst spot possible. Here is a diagram of where the connector is for the front wires (it's mirrored for both sides):
View attachment 524946
Now look where the rear doors clip into (I decided against wiring them up, I like camping in my Model 3 and they might get annoying anyhow):
View attachment 524948
Now a real life picture of the front clip for the front door pockets. I found it easier to unplug this to work on it. Be warned if your car isn't off, it will nag you about using the manual door release if you unplug it. Push the black tab it and it comes out easy.
View attachment 524953
Now, with the harness uplugged, the fun part begins, you gotta pick the right wire to cut. On both sides, the wire is red, but the pin position and wire colors of the neighboring wires differs. Here is the driver side just after I snipped the connection.
View attachment 524954
Now just wire up your 12V power to the wire that ISN'T connected to the harness clip. That will feed straight through the door and to the map pocket light. You're probably wondering how the heck you'll know what wire to cut, and the answer to that is easy. It's on the back row farthest from the black clip. I've mapped out the wires you need and their two neighboring wire colors and sizes. My writing is terrible, but I think it's readable. I've only confirmed that this is accurate for the front wires, but I think it should be right for the rear ones too.
View attachment 524960
And that's it, you're done! Well, more or less. If you're brave enough to attempt the rear doors, please post your experience and I may try it. I took one look at the harness location and said "nope"! I originally had a hidden switch I was going to mount to the driver side kick panel to allow me to kill the ambient lights on demand, but after seeing them in person I don't think they'd be bright enough to warrant turning off, so I might not bother doing that after all.
If you're one of the wealthy people who has a 2020 with a premium interior, I've heard your door pocket lights may be disabled but still present. The conclusion seems to be that Tesla cut the wire in the door panel itself, so you'll have to pull the panel and rewire it in that case. I'm assuming later models will also be missing the light, so you'll have to buy that if so. Your mileage will vary!