I can't help with a diagram but are your sure it's a wiring problem and not the wiper motor at fault? I ask because I have experience of an early wiper motor (1994 van) where the copper tracks that control the wipe speeds etc (similar to a printer circuit) can crack. I repaired mine simply by soldering across the break in the track. It's an relatively easy and cheap fix if you know how to solder.
recently helped a friend with a wiper problem - wipers would stop
turned out to be the spindle going through the drivers side bodywork
eventually freed it up with copious amounts of wd40 - had to remove wiper arms to get at the spindles & seem to think I had to remove a plastic seal to get the wd40 down to the spindle which was dry and sticking
I have had an auto electrician look at mine was trying to get a wiring diagram. That was weeks ago. I have a 2005 Ducato. Happy to buy a wiring a service manual or wiring diagram.. Can and borrow or even steal one.. Ha Ha will buy.. There is one on line but very poor information.
Hi John and welcome to MHF, you are on a quite old post, but if you do get any info please post it as that is what this form is all about normally, Brexit and Covid19 has 5aken over a little bit, but we'll get back to normal soon hopefully.