Unimog Club UK

If you get a chance I would recommend watching this on amazon....

Trailer available on YouTube: https: www.youtube.com/watch?v=yPKR4UM4RSc

Not as much as I'd like, but....
I've been hidden away in the shed getting the engine up together.
I have a set of replacement connecting rods as the threads in one of the originals were a bit knackered! (appears its been apart before..)
376-030-71-20-40 Connecting Rod For OM352 HMMH
They are M12 bolts. The om352 manual specs 90Nm, does this sound about right?

They appear to be the same as 366 030 3520.
Thinking the part number 366 is for the om366 series engine (longer stroke?)The internet says step 1: 40-50 Nm then step 2: 90 degrees

Tim, I did the same. The mog had been sat in a barn for nearly 14 years before I got hold of it, deffinatly get it up and running to start with. You'll soon find out what needs doing. I'd been driving it around for nearly 3 years before a broken spring and leaky hub seal finally made me start the rebuild!

I'll find a pic. The metal work wasn't too bad under the various layers of paint! 
The usual, under the headlights, roof hatch, under the window rubbers and the passenger side floor (Windscreen leak..) have all had new bits welded in. The roof was full of filler, allot of the dents pulled out quite nicely...
Hmm, that is only the etch primer, and under seal. A lap of primer then top coat to go!

Next will be the engine, I've a re-honed block in the boot of the car!
The list goes on and on from there.. 

I fitted new secondhand tail lights and a new trailer socket which had to be rehashed into a mess of old corroded and cut and broken cables, all previously joined into a rusty old junction strip.

It does at least sound like its all original then! 
The factory extras seem a little sub par in build/assembly quality!
I don't know how my trailer brake valve has survived this long without falling off, looking at the welding on the bracket!

I've had the cab in the garage since October, just making a start with the etch primer!

Regarding the Diff lock lever and solenoid.
The solenoid valve your looking for is mounted on the top of the gearbox at the very back, look straight down inline with the back of the cab. You can see it in your photo of the back of the cab!
There's 2 air pipes on the valve, 1 of them splits into 2 disappearing off down the torque tubes.
The other heads back to a valve of sorts, I believe it only lets air through at a set pressure. Possibly more than your 4 bar.. 

I'd be checking the lever is all the way up, has it made the 3rd indent looking underneath the cab?
From my own experience the rubber boot on the solenoid goes extremely hard, stopping the plunger operating.
Take a measurement across the plunger before and after you've engaged the hand lever, has it moved?