Update
I have found a fuse which was blown, number 11 a 10amp fuse which I replaced and everything was fine again until I drove it a very short distance and blew again.

I have got the wiring diagrams and the associated relay is 1389 which is fine, the modules linked to the fuse are 319 the heating control unit, unplugged and no difference, the module 645, and the 2086 which I can not find even though I have location diagrams for is.

Does anyone know where the 2086 module is?

 

So I got another bcm with the same number with the intention of getting it cloned.

Before I send it away, I plugged it in and the fuse 11, still blew, now my reasoning is that even if it's not coded it should not have the short (if a short is inside the bcm) and there fuse shouldn't blow.

As it still blew, it leads me to believe that the problem lies else where, the fact that the fuse only blows when the bcm is plugged in at least the long plug and the black power plug, there must be an internal routing in and out.

My wiring diagrams are dubious to say the least, does anyone have wiring diagrams for the 2018 Renault master or have a link to a visu type software? I can only seem to find the visu software that cover up to the 2008 models.

 

The visu is on line at Renault Net for your year
645 is your Body control module

Can you disconnect the power steering electrics under the dash to see if its that area

 

Yes I did that already, it made no difference as it's run of the usm and that goes down when the Bcm does.

I unplugged R260 above the cab which feeds the rear lights,rear brake sensors and the fuse is holding(for now, been here before on another place and it returned) fingers crossed this is where the problem lies, it would make sense as the rear has been heavily modified when converted into a horse box. They haven't made it easy though, the rear lights are a pain to get off to unplug and the wiring has been hidden behind various riveted panels.

I don't seem to have a diagram for the plug and its pin out, so finding out which line from the plug is shorted is going to be a challenge.

I have pin extractors but they don't seem to work on those big lever plugs.

 

Update

Found the line the short was on and I have isolated it so the fuse 11 no longer blows, however im not entirely sure what this line was connected to, it was a red wire.

So now it doesn't blow when I plug the bcm in but I still have a brake fault and steering fault showing up, so scratching head as to why, I thought that when the fuse was stopped from blowing and the bcm was working all the faults would disappear, the hybrid power steering is still not working.

Does anyone know if the bcm can be reset from disconnecting it from the battery for a period of time?

 

Update fixed.

After a lot of tracing I found the abs pump was not getting the 12v power after ignition to pin 28 on the big plug. I traced this to a blue and red wire from the bcm which had broken on the top of the dashboard. This wire comes up from the bcm and heads off to the left hand side of the van.

Once this was reconnected all returned to normal, no abs light and the power steering worked again.

Why the power steering fails when the abs fails is madness, instead of a bad situation you end up with a worse situation in trying to get the vehicle to a safe location.

So what started with a short In the cables at the back of the van which caused fuse 11 to blow and loss of abs, esc and power steering resulted in another problem to some of the same areas causing massive confusion, I can only assume that I broke the second wire in fault finding the first shorted wire. By the looks of things I'm not the first person to have been looking through the loom as it was not as It came out the factory.

On further investigation I found that when whoever converted the van to a horsebox (well I know which company it was but I'm not going to name names here) cut something off the loom and didn't properly isolate the remaining wires and there is not cable retention of the loom, it's just loose behind metal panels which were riveted in, a stupid decision in my opinion, no thought to future maintenance and faults such as I encounter. The conversation was only carried out last year and has not covered many miles since, so there really isn't any excuse more than just shoddy craftsmanship.