I might be able the shed some light here. First of all, the ratings on your trailer are in metric. However, I would not worry about overloading it, because the axle is rated for 4 metrics tons I think and just look at the construction. The only thing is they have a really small maximum tongue weight. You could change this trailer over to overrun brakes if you get the parts for it. They came this way from the factory too, would save you messing with your mog. So as for the type of gladhands you’ve got: The black one is for a single line trailer brake system (not to be confused with the single line hydraulic brake system in your mog). In this system you connect truck and trailer with a single air hose. While driving the line carries pressure and the valve in the trailer directs it to the trailers air tank. If you start braking, the single line valve in your mog cuts the pressure supply to the black gladhand proportionally. The valve in the trailer senses that and stops charging the air tank. Now it uses the air from the tank to brake the trailer. However, the air does not get replenished until you stop braking. This system was popular in Germany in the 50/60s because it was simple. However, the major drawback is that once your trailer air tank is empty you lose your trailer brakes until you stop braking to replenish the supply. Which is bad for longer descends. So it has been outlawed in Germany for anything faster than around 15mph. This system needs another valve configuration in the trailer too and another operating pressure, hence there is usually a second pressure regulator or one with two outlets on the mogs. The other system is the more modern dual line system matching the one on your trailer. The red system supplies the trailer with air to its tanks. And the yellow one relays the brake signals which get interpreted by the valve block mounted to your trailer. The other manual valve lets you set how hard the trailer brakes according to how heavy its loaded. From full power towards the brake valve to no brake at all “Lösen” towards the tongue. As for the systems you’ve got for your mog: The older one that actually came from you Mog is from the 60 or really early 70’s I guess? This is the setup that properly fits to your mog with the single circuit hydraulic brakes. The main part are the two main valve body. The one with the one with the two ports on the side one in the front one in the back is the single line valve, which is mounted on the passenger side. You could basically delete that. It doesn’t work with your trailer or probably any trailer you will encounter. Nevertheless, just to be complete: The lever is the handbrake, the input on top is for the air signal from your brake booster and is connected to the closest top port of the other valve. The input in the back is connected to decreased pressure from your air tank via another pressure regulator. Finally the last port is the one going to your black gladhand. This leaves you with the dual line system based around the other valve block. The first puzzle piece is the red gladhand which is connected directly to the vehicle air tank or usually on the side port of the pressure regulator used for the single line valve. An important feature of this gladhand is the cut of valve, because there is no valve in the gladhand itself meaning it would just vent the air if nothing is connected. However, that’s not all There is a little T between the shutoff valve and the gladhandle. It gets connected to the top port on the dual line valve the furthest away from the hand brake actuator. This is the input for the air that is used on the yellow signal glad handle. Which is directly connected to the back port of the dual line valve. With this set up the single shut off valve shuts of the air to both gladhandles. The final part of this system is the actuating circuit with your brake booster. There is the port on top of the dual valve closest to the hand brake actuator. It should be fitted with a t/fourway splitter. One goes to the signal in of the single line valve. Which can just be blocked off if not in use. Another output, usually the front one directly goes to you brake booster. If I remember correctly into port “A”. If you apply your footbrake the first chamber of your booster gets pressurized and port A relays that pressure to the trailer valves. And you already noticed that there is a U connecting to ports on your booster. It leads to the second chamber in your booster, which when supplied with air makes your Unimog brake harder with the same brake input. This U is removed and replaced by a line coming from the last free connection on the t on top of your dual line valve. However, it’s not a direct connecting. The final manual shut of valve you showed for this old setup its put in this line. Its purpose is to shut off the airflow to this second chamber in your brake booster. If I remember correctly you close this valve when attaching a trailer so your mog brakes less/later in the pedal travel. This intern results in the trailer brakes breaking harder than your truck keeping your rig straight so the trailer doesn’t push on your mog. Additionally, you showed the other setup, which I would guess is from a never mog after ’72 or so. When Germany, France and other nations started their proto concepts for what’s now the EU, they also started standardizing air brakes to make shared traffic easier and bring safety to the same standards. This is the point when the Mogs started to be equipped with dual circuit brakes too. For the trailer brakes on your mog this means they have more safety features. I don’t have their complete setup in my head, but the come with load sensing and valves detecting when your trailer lines detach, etc. I also think they changed how/when your lockers and other secondary air components get pressure (in the old system is just a valve that opens after a certain pressure). All in all it is based around the same valves, the same system but with more components to make it safer. You find this system as “EG” Bremsanlage/brake system in manuals If you just want to pull this small trailer occasionally, I would recommend you install the older system. If the old dual line valve does not work you can disassemble and clean it or use just the valve from one of your other sets in the old setup. They work the same. You could even go as far as just buy a new standard dual line valve from a truck parts store. They only thing is they are quite rare with mechanical parking brake actuation. There are work arounds for that however, using the single line valve as a hand brake vale or just using an additional hand brake valve. When used reasonably the old System works fine too. Especially on the mog, because for one: even if you loose air pressure you may lose trailer brakes and brake booster, but not your brakes. And even if your trailer brakes fail: The Mog is rated to tow 1,5 metric tons without a trailer brake. So if the trailer is not too full you don’t even need them technically. But be careful, the mog is pretty light on the rear axle so it sometimes like to jackknife if the trailer pushes. I currently got the air schematics for a 421, so the little brother of the 416/406 on hand, but also only for the old-style brakes. They are pretty similar between the two. If you drop me a contact information I could send them to you. For any further questions I would recommend the Unimog-community forum. It’s mainly in Germany, but people are welcome to post in English too, that’s no big deal.
Do the valves or pressure regulators have any marking to give you a clue to what type they might be? Looks like a trip to your local truck stop, Amazon. Grote also has a wide range of tractor supplies. Good luck.
