I'd like to thank Tony and Kevin too. Like a fool I've just realised that I could have taken photos while I was doing it. Too late now, it's back together. But I'll give a long wordy description of what I did. Hopefully the more words I use the more likely it is to get picked up by search engines.
So, I've got a Whirlpool AWZ 121 tumble dryer, with a start switch that wasn't latching.
First, take the top off. There are two self tapping screws (on mine they are T20 Torx) which attach it on the rear. And clips on the front.
You can now see the business. Like the others, you don't need to remove all of the front panel to do the job. In fact I couldn't work out how to detach it at the timer end anyway. What there are are a lot of plastic clips which attach the plastic front to a steel sub assembly onto which the switches are mounted. Detach that as much as you can.
Take out the white switch. There are a couple of plastic clips on the left hand side (viewed from front) that you'll need to push in to get it out. Then lift it up. Now you can see down. There is a brown thing which is spring loaded. And a sort of mini maze of plastic. In the end of the brown thing is a hole, into which one end of the wire should go, the other end into the maze.
I actually pulled out the brown thing, to save having to take the white button off, but careful you don't lose the spring. Then you need to make a U shaped bit of metal, using a (thinnish) paper clip. EXACTLY as per Kevin's dimensions. The 15.5 mm is the bottom of the U, the short bits are the uprights.
Thinking about it, you don't actually have to take the switch out to fix it, just the electrical bit. But it does mean you'll be putting the re-modelled paper clip back in from the top, so get your strong specs on and good light.
But if you have taken it out then, to quote Haynes, 'replacement is the reversal of removal' (yeah, right!)
Leave the top off while you test it. But careful with that electricity. And remember that drum will spin.
Mike, October 2012