Problems starting - just a click

[lew15]

Thanks. 14 pin connector seems absolutely fine. Where are the earths at the front? The 'crown' ones behind the fusebox? If so they looked OK when I checked them last week.

Battery connections seem fine too. It's a new battery and they are clamped on well. I'll check the earth strap underneath when it's not raining.

Pic of my engine bay and a couple more questions:
 https://drive.google.com/file/d/1hjS__V ... sp=sharing

Are the oil pressure switches buried somewhere in the area I've circled blue? Are they easy to check the wiring's OK? Think I need to remove a cover?

In the red circle there is a wire going to a rubber booted red plastic plug. What is this?

[Stesaw]

Oil pressure switches will be left hand side of the engine as you look at it from the back. Low pressure switch is underneath between the pushrode tubes, so you.might have to remove tinware to see it, Should be a black switch. If you have a high pressure switch it will be below the water pump pulley facing the back of the van. I think they are grey usually.

[TwinTurbo]

Work back from the fault, not towards it. 

bridge main terminal to solenoid (test)
jump lead from chassi to gearbox (test)
jump lead from batt to main terminal (test)
and so on

[weimarbus]

Have had a similar issue with a new chinesium starter, the solenoid appears to need a higher current, replacement ignition switch made no difference, but would start readily when bridging the starter main cable to the solenoid connection, have installed a relay in the engine compartment to take the load off the ignition switch and starter cable to the motor solenoid and no more issues (fingers crossed). 

[tandemsandy]

Had similar, also a 1.9 DG.
I'd added a relay to the trigger wire a few years ago.  Then got the 'click' but no action from the starter.  Turned out it was the solenoid -  it was being thrown, hence the click, but the big heavy copper contact in the end was worn, so not closing the high current circuit to the starter. Can test for this by a continuity check across the high voltage terminals when the ignition key is turned.
On a DG you can (with a bit of jiggling) replace just the solenoid without replacing the starter itself. I can find the Bosch solenoid part number if you want to try it. 

Rob