I changed the engine filters yesterday, including the fuel filter, and only half filled it with fresh diesel. I expected to have to crank it a while, but after 5 long cranks it stopped cranking.
I've checked the fuse and relay R10.
When i short the relay connectors for the starter it turns over nice and quick, but not on the key
I swapped R10 for another relay and thought that fixed it, the first cranking worked, then it stopped turning over again.

I pulled R10 out and checked the pins. Pin 86 of the relay (high side switched ?), floats at about 2.75V with the ignition on, and when the key is turned it once or twice jumped up to 12V but does not do it reliably. I still hear a slight clicking when turning the key to start the starter, but not sure if that's coming from the passenger fusebox or engine bay one

I can't find a wiring diagram online, what device switches terminal 86 of relay R10 ?

Cheers
Chris

Hopefully this will help.