Hello Andrew,
Slightly off topic I know, but this is a problem which I have been having lately where you have to think "what monkey has been here before me?" I've just done a year 2000 Iveco Horsebox with faulty main and dipped beam lights and cranking/starting issues which has taken over 9 hours to repair because of somebody else's attempt to a short lived repair, luckily though the owner is happy to pay.
I don't like to be beaten so came to an agreement on price.
Not wanting to pry too much but how will you be charging out such a job?
Ian.