Im new to the forum here, so please be gentle. If I am posting in the wrong spot, please let me know.
My issue: I have a 1993 Audi 90 (non quattro) v6 5sp which I recently acquired. The car overheats due to the fans not turning on. At first I was loosing coolant because the reservoir was cracked, I replaced that and found that the car was still overheating and noticed the fans do not come on. Also, the heater core is bypassed (in case that matters for anything). So far I have checked: the fans- when connected directly to power they run just fine; the relays for the fans that are present have been tested and are functional. (though there are some suspicious spaces in the relay panel where I am not sure if there are supposed to be relays there.); the temp switch in the radiator was tested and is working as well. I thought about trying to bleed air out of the system but don't know where. I let it run with the reservoir cap off for a while, but I don't know if that will bleed the air or not. I have run out of things to check.
There are a couple anomalies which I am not sure if they are a factor or not.
First: there are several missing relays in the relay box. Some of them (according to the pretty picture on the top of the box) are supposed to have something to do with the cooling fans, but I can't find documents/schematics that call out what those relays are and if they are actually necessary in this vehicle.
The other is a mysterious red plug on the passenger side right next to the radiator that doesn't plug into anything. I have looked for a mating plug and wire harness for it, but it is not there... again, not sure if this is required for anything or if it is a provision for another configuration of the car.
I uploaded photos of these as attachments (i hope... not sure if they made it)
I have tried to be as thorough as possible with my description here, now I ask for someone who knows these cars to help me out. I have run out of options, and do not know what to check next. If there are other components to check, please let me know, with photos if possible, where they are at. I am new to the audis and am not familiar with their components.

Thanks

 

Looks like in picture number two you are missing a component of the AC system. Looks like a plug for a pressure or temp sensor.

First photo, you should have a fuse and relay guide on the fuse box cover. Thats how it is on my '91 90. You should be able to determine whether or not the missing fuses and replays apply to your model. I.E. options, diesel, etc.