OBD Port has no power?

Below is the F5's entire circuit, it comes from the Immobilizer into the Fuse Holder 2(Fuse F5) then just goes right back out to the Instrument Cluster. For some reason F5 is missing from the aftermarket power diagram altogether, they forget things a lot. But I found it on the Cluster diagram below. Going back and forth through these diagrams, the OEM and aftermarket ones for this specific car are very difficult to read.
But only for F5 right now, you can see in the first diagram it comes in on X10199 and goes right out X10200.
It even shows you the wire color it should be, so black wire with yellow stripe (x10199) and then a Black wire w Violet stripe (x10200). So, you could find those specific wires on those connectors and check them for power. That will tell you if the power is being lost in the Fuse panel (Fuse Holder 2) or if the power is not even getting to the fuse panel.

I've been trying to find a pinout of X15 for hours and just can't seem to, if you can ID the pin that broke and the two wires in connects together, if this was my car, I'd just bypass the connector, but you have to be used to doing electrical work on vehicles. I mean it's only a connector and it's full of corrosion. I would cut the two wires and crimp them together with a heat shrink connector and be done with it. Just do one at a time so you don't get mixed up.

I'm not sure you'll be able to find one of those connectors, maybe a dealership, or like you said a used parts lot. I'm not sure how many you have in your area. Now that a pin is broken, it has to be fixed, but our main concern is getting you through inspection first. They will probably fail you if there's no Tach lighting.

So far I've found that X15 is for the Instrument Cluster control module, but they don't give any information on it.
For the Cluster (diagrams 4 and 5) you can see they don't give us barely anything. It shows the connector and wires to it but doesn't show anything about the Cluster at all. There's no Tach listed, so I couldn't even tell you which wire it was on.

So, it really just depends on what you want to fix first, let's concentrate on one area to get repaired, then we'll move on, instead of jumping around.

Okay, were you able to make a good strong connection for Tach light circuit, when you crimp a wire after you strip the end insolation off, the crimp has to be as tight as you can get it. If you can pull it apart with your hands, it's no good. A rule of thumb to go by. And using the heat shrink connectors will keep any moisture out forever, you can get away with using a lighter to heat the shrink on the connector but be easy about it. You don't want to burn it; I use a small light Butane torch to just barely heat the connector up. Glad you were able to figure that out.
So on to the next, we will call them marker lamps to stay on the same page. Do you have both front and rear on the right side out?
On the left (driver side) you have your 1. Turn signal front, 2. Front Auxiliary Flasher Light (another blinker) 3. Side marker light, 4. Rear side marker light 5. Parking light. And then in the rear there is the Left Taillight assembly which has 4 lamps in it, Parking Light-Turn-Brake-Fog Lights. I'll put up the diagram of them all below.
So, if the problem is isolated to the Left side, since there are so many bulbs, if you can tell me the wiring color for the bulb socket that is out, it will make it easier to identify which one is not powering up. That Taillight Assembly is all housed together and uses one shared Ground wire coming out. Unfortunately, every single bulb has its own single wire coming from a General Module Control Unit as far as I can tell, I haven't looked at the OEM diagrams yet because for this vehicle they break them all up into small sections and they're very difficult to trace out. The General module is located in the Right Footwell, so it's on the passenger side but in the same place as the fuse panel with the corrosion issue. Hopefully, this is not the windshield leaking and we will find more corrosion on the passenger side. The module has 4 main connectors, some of the connectors look to have a bunch of wires and some only have a few, so pull that panel out like you did on the driver side. We're going to have to look for more corrosion on the passenger side. The diagram below is for all the exterior lights on the driver side except the Head lights, there are no specific fuses for any one lamp, there are only fuses for the module that controls them. We might end up in another huge mess on the passenger side, so I would keep looking into that Fuse panel and see if it comes apart or keep an eye out for a new/used one. I'll look into this module some more and see how it works, I'm a bit worried it might have issues with the connectors on it as well.

On a side note, the Switch Panel and the Turn Signal/Head Light Dimmer Switch that are wired into this General Module Control Unit for the exterior lights both have a fuse that runs into Fuse Holder 2, that's the one on the driver side we've been dealing with.

The General Module also has 2 fuses running into it from Fuse Holder 3 in the engine compartment, just wondering was this an auction car?
Also, can you find a Manufacture Build date on this car, it might be on a tag in the driver side door opening, or under the hood on a tag. It will give a month and year (ie 12/03 or 12/2003 for example) because a lot of these OEM diagrams are listed differently for different build dates.

Okay, I think these are the ones you have out, that Brown wire is going to be the Ground for all the driver side exterior lamps. But as you can see, there is an error on these diagrams, marked in 'Red'. They labelled two pins 29 and two pins 5. You can check to see if you have any voltage at all on the Green/Violet wire, which will be the feed. If there is something more than zero volts, we have a high resistance issue on that wire, if it reads OL on your meter, we will assume for now it's an open circuit and have to test it at the module pin. I've got each connector on the module already labelled, so for these 2 lamps for example, it will be connector x254 for the Rear lights, And then for the Front Lights, is it possible it's the Low Beam that is out, because according to the diagrams both front Fog lamps have Yellow and Brown wires and the Low Beam has a yellow/green and brown wires. But at the module we will have to go by wire color somewhat, I don't trust these diagrams completely.

Anything that is out, take a voltage reading to see what type of condition we're dealing with.

That's great news. I was wondering how you made out with that. Just make sure to do the water test so you don't end up with the same problem down the road, no pun intended. I see a sunroof option in the wiring diagrams, so if you have one of those, make sure to run the hose over that too, maybe have someone else run the hose so you can watch inside for any water drips coming in, since you know where the problem area is now. Keep that panel off that hides the fuse box and watch up above it for water. There must be a leak for the box to have gotten that bad. Just a precaution. Hope your inspection goes well, you might also think about erasing any stored codes before going and then drive the car for a few days so all the readiness monitors have passed. That way you'll only have to go do inspection one time. I know that was a lot of work on your part, but thanks for letting us know the results.

Hello again. Yeah, the seat belt light on the Instrument Cluster will come on if the sensor in the seat belt latch is not sending a signal to the Restraint system that it is buckled in. There isn't any other lights on are there, such as the SRS light or Airbag light? The sensor in the driver side seat belt latch is a hall effect sensor. So, it will have a power feed (12volt), a wire going to the Cluster (that's the one you're seeing), a signal wire to the Restraint system and a Ground wire that is under the center console. These systems have seat belt tensioners built into them that will react when in an accident. With the airbag, you have to be careful working on any part of the system.
With all the water intrusion you had I'm not surprised more issues are showing up.
And of course, the power for the seat belt sensor comes from the Fuse panel you just replaced. Fuse F18 5amp. I will try to locate exactly where the sensor harness plug is. Most of them are down on your right side where you latch the seat belt in, you might see 4 wires or a section of harness coming out the bottom of the seat belt latch. I'm guessing it might be missing power as so many other things were. When did this start happening?

Looking at BMWs safety instructions, they insist on having only qualified BMW personal to work on this particular system. And this is something I agree with, if an air bag system is triggered by accident it can cause serious injury. This includes even the Seat belt buckles. They are listed as "Pyrotechnic object danger class T1" Which is one of the highest levels. On some Seat Belt Tensioners there is a small charge in the tensioner that will lock the seat belt in the event of a crash.
They list an Airbag Deactivation switch, but do not say where it is located. The battery needs to be disconnected and isolated as well.
I have seen these go off by accident, and its thousands of dollars to replace the airbags.

They require a Terminal Kit to test the Seat Belt Buckle Switch as well using an Oscilloscope. The kit does not actually buckle the seat belt, it's strictly a testing kit (fifth diagram)
So, this is one I would recommend having possibly the dealership look at, I'm not even sure where they get this 4-pin terminal kit. Thats what is needed for the hall effect sensor buckles.

The sensor is probably missing its 12v feed, I can look into what connector it's on, and if it is part of the X1 I'd be okay with you fixing that, since you've already been in there. My only worry is the signal wire for the belt buckle goes directly into the SRS system, and a voltage spike into it would not be a good thing at all but give me a few minutes and I'll take a look.

Ok, you were correct, it looks like you might have hooked the wrong wires up on that connector, which is x15, not x1. But I finally found the issue, I think you may have just hooked a power wire directly to the seat belt light wire.
The diagrams below 1 to 4 are the power wires going to the seat belt sensor and are the power (12v) to the sensor.

But the wire that goes from the seat belt sensor to the Instrument cluster light does go through x15 connector, (diagram 5) is the oem diagram and shows x15. Diagrams 6 is the pinout for the x15 connector,
So you may have it hooked up to another wire, but if you look at diagram 7 the aftermarket diagram label the wire as Blue/Yellow.
The oem diagram looks like it has the wire to the Cluster as colored Blue/Green. And I know after awhile the wire colors can be very difficult to see correctly, they fade and can be misleading.

Im not sure I would go cutting any wires yet, but take a look at the x15 connector and that pin 28, it should be Blue/Green going in and coming out. If its the incorrect and wired wrong, thats the aftermarket wiring diagrams fault.

I run into this alot, miscolored wires can cause all kinds of issues, like we have here. But thats what is happening. You didnt cut anything with the connector in the 1st diagram, so I think its only the wire going to the light on the dash that might be wired wrong.

Yeah, that's a bummer that even the OEM were not exactly correct, yes ill see what color the oil pressure sending unit is to the cluster.
Both diagrams state it's a solid blue wire. It does of course run through x15 and then up into the center of the dash and around then back over to the cluster. The second picture is the location of the oil pressure switch. You have to remove the right front tire (passenger side) to get access to it. But it looks like a solid blue wire all the way from the sensor.

There is no definition on exact operation of this specific oil pressure switch, but it provides the ground connection for the oil pressure led in the Instrument Cluster. The power for that led comes through the cluster and when the engine is started, the oil pressure switch either opens the circuit to turn the led off, or it pulls the circuit to ground to shut the light off.

So, what you could try is since you're going to recrimp it anyway, either unplug the sensor or cut the wire and see if the oil pressure light goes out. If it does, then that's what the pressure switch is doing, it would be a normally closed circuit and oil pressure opens the circuit turning the led off. It might be more practical to unplug the sensor behind the passenger side wheel. It's a 1 wire sensor running into the engine block and the wire is Blue there too. But that's up to you.

On one diagram it looks like it's a pull-down circuit and on another it looks like a pull up design. But I know it definitely makes ground for the light on the dash.
There might be another circuit coming off the led going to the engine computer. But in that case the car would usually not start. Most are designed so that if there's no oil pressure the vehicle won't start.
But I would check your crimp first, Ill track down the rest of the connectors for the sensor. There's one in the engine compartment.

You can check either half of the blue wire for voltage, checking voltage won't hurt anything. Because it's a led in the circuit I don't think you're going to see voltage, a led is a diode and diodes only let voltage go one direction,
If you're checking the resistance of a circuit, it is when the multimeter puts out a small amount of current to check resistance, but everything needs to be unplugged to do that or you will end up reading the resistance of the entire circuit. And for example, with an airbag circuit, a multimeter can actually set off an airbag. So do a voltage check if you want to, but I would just check the crimp, see if the light goes out. And I'll get the rest of the connections for it.

Yeah, glad you got most things straightened out. I'm surprised at how much work that car needs. Hopefully you have heat at least.