The trouble with making things idiot proof ....

 ... is that they keep making more extreme idiots.

QED (1)

A year or so back I lent my trailer to a neighbour's sons.  On their second trip to the tip a wheel fell off at 80 kph and disappeared into the bush.  5 of us searched for hours and couldn't find.  I had a spare wheel which they fitted and all worked, but I no longer had a spare.  

The trailer people wanted $250 for a new wheel, and I reckon the trailer was worth about $50, so pass.

Wreckers had been hopeless.  So every time I went to a landfill I checked for thrown away 4 stud wheels.  Then I got lucky and found a discarded trailer with a 4 stud wheel.  This - the wheel - was acquired.  The centre of the wheel was great and actually fitted the studs on the trailer's hub, but it was 13", rather than 14" as were the other wheels on the trailer  This didn't seem to be a problem while driving, although conceptually it should have been.  A friend then said that I should check the second wheel on the decrepid trailer!  Dooohhhhh.  

I now have two wheels the same size (13") on the trailer and a 14" spare (also mounted on the trailer) .

QED (2)

While driving the Pajero somewhere dusty (or muddy) I found the rear window washer was not working.  I thought this probably meant the jet was blocked but couldn't spot the jet to clean it.  So I was trying to find out how to remove the spare wheel, as that is where I thought the jet was hidden, and found the arrowed strange fitting.

On consulting the manual - Doooooohhhhh!, when all else fails - it turns out this is the filler for the rear window washer.  We have had the car for some 10 years now and I had never realised this, but had assumed there was a pipe from the reservoir (in the engine bay(  for the windscreen washers.  I presume that this reservoir was filled up when the car has been serviced in the past: whatever.  It now works again and in fact shows that the jet for the washer is on the top of the rear window and nowhere near the spare tyre!.

I repeat Doooooohhhhh!💀