Try these people they do lots of nice kit https://www.caktanks.co.uk/

Change the earth strap then you have a know good one as they rot where you can not see they are a common fault, located passenger side engine mount area.

Rangeroller DT is good with bolts and stud extractors :vb-biggrin:

Wandering steering can be the radius are bushes, they should sit in the center of the axle mount if you can move them sideways with a bar they are shot.

Yes that was one of the 1st things I did. I did not mention it but I actually have an extra box to avoid rf noise from nearby sources from Marty.

Have you tried using the key fob next to the rear window to the right hand side of the tail gate as the ariel for the RF unit may be disconnected to stop battery drain.

But beware the license expiry. Quite a few reviews on amazon saying it's cheaper to buy a new one than renew the license in the App !!

Trailer wiring at a guess,

12.15v is very under 12.4 is considered a dead battery what are you getting at the battery.