AAAAhhhhhh Ok. I thougt the "module" you were talking about was the trailer lighting module in the Disco.
- Without the "processor", your trailer lights go disco?
- You presumably therefore have the trailer lighting hooked straight to the loom? (i.e no module in the Disco?
- I don't know the DIsco to this level, but how does it do bulb failure indication? Beeps / Lights on the dash as in the old relay style or do you get an on screen message / fast flashing like a lamp on the Disco has gone?
I'm going to take a slight tangent here.....
Where does the cabling to the socket on the hitch come from?
You said the park sensors etc didn't switch off etc. That says to me that the Disco probably should have a module that it doesn't have..... Was the hitch a delaer fit?
I got the place that sold me my Mondeo to fit the hitch. After three separate "and you are absolutely sure this is the dedicated Westfalia / Ford Can talking module?" questions (....'coz I can't buy the module for the price you are offering to fit the whole lot for so I am a bit suspicious)..... and guess what. I plug the trailer in and out of the boot comes "beeeeep.....beeeeep.....beeeeep......".
"but it is for the Mondeo sir, look......" (yep, and for every other car on the planet that a bypass relay will stop the lamp failure warning flashing.......
I think you might be missing a module.....
Land Rover Discovery Towbar Wiring Kits
Looking at this if you have a Disco 4 the fitter would need to have poked your can bus to tell the Disco the module was present....
FWIW I got one of these fitted.
Ford Mondeo All Models 13 Pin Dedicated Wiring Kit Jun 2007 on 29060515RC
(note it has a "yes" on the Trailer LED box, but go up a level in the shop and not all Mondeo modules do - so you canlt generalise!)