I can't have a trouble free day.

With the battery sitting pretty and nicely charged I thought I'd better give the old inverter a run. Hook up the leads, sparkle, hmmm don't like the look of that, switch on, nothing!
Argh it seems the old Hodge luck never changes, leave it for a while, do something else.

Open it up and see nothing obviously amiss, decide I probably wanted a new more grunty one anyway so order one, at least they're not expensive these days.
Look a bit more into it, it seems the sparkle when connecting was just the pair of capacitors on the right of shot that charge up as soon as the leads are connected, regardless of being switched on, so that lead to some simple head scratching leading to the obvious, check the switch! Bingo the switch was faulty, to be fair about it this inverter has been under floodwater in the past and this may have caused resistance dramas in the switch, anyway I was very impressed by its simplicity, in the past daring to dismantle a switch usually resulted in endless frustration with springs and things going every way they want as long as it's not the way you want. This one was great, clean up the contacts, add a little silicon grease to the pivoting and sliding bits, then success, Now I wish I hadn't rushed into that order.