after the Park Life Blat, this morning I set about fixing my non-functioning brake lights...
the switch is OK (but I also have a replacement) - closed circuit when plunger out, open circuit when pushed in
bypassing the switch with 12V lights the rear lamps
putting 12V on the switch and closing it (ie letting the plunger out; either switch) lights the rear lamps
however, the feed to the switch has 12V on it
but when I connect that to the switch and close it, the rear lamps DON'T light!
similarly, if I short the feed to the switch to the output, the rear lamps DON'T light.
it is almost as though there is 12V there but insufficient current to light the rear lamps
is that possible? if so, what would've caused that to happen (ie what do I need to do to fix it?)

That would suggest an issue with the normal 12v feed.
When you connect that, and the switch is 'closed' does the 12v feed vanish?

sorry missed this (hadn't got notifications turned on I guess)... yes the 12V disappears from the feed terminal

Ok, then that really does suggest a bad connection in the feed circuit.
Could be a broken wire, that is 'just' touching across the break.
Or a dirty contact in the feed?
Basically, a high-resistance that can show a voltage with no load, but causes the voltage to drop to zero under load.
(And what an arse that Arnie is!)

I reckon all that too... wouldn't be surprised if there's dirt in the connector given the nasty weather we had last week.

Can't comment on M Du Lard - have never met the chap but he's being helpful (as Jonathan Kay et al often are on Blatchat!) so will reserve judgement!

I was commenting on his initial comment in the Facebook thread - not at all necessary, nor of any relevance/fact...
That does make him an Arse in my book!

ah - got ya!

Language

Good point Hatter... so the automatic censor won't allow use of the word ********** but will allow such improprieties...!

It seems a tweek might be needed Colin

Found the issue yet???

Nope...
I've added a separate live feed to the brake lights as a temporary fix, Like all temporary fixes, it has the likelihood of being permanent!
The investigations I've made and the wiring diagram seem disparate... I disconnected the relevant pin on the 6-way connector and there was still 12V on the feed to the brake light switch, suggesting that either I've misinterpreted the diagram or there's a short elsewhere or....
In all honesty, I ran of out time and was getting bored with it!