Hello again guys
All fixed now. I found the switch, but had no idea how to remove it. In the end I reversed the mower up a make shift ramp, then put plenty of bricks underneath it to ensure that it wouldn't be able to move or drop on me, and then stuck my head underneath. Once I could see it became fairly clear that it was just a clip in fit, and a flat bladed screwdriver soon did the trick to prise it out. The switch worked when I tested it on the bench, open when relaxed, and closed when depressed, and I also noticed that the switch must be in the open position to detect the basket. Closed, which I checked by jumpering the open ends of the leads, caused it to think the basket was missing, and engaging the pto would then stop the engine, just as it should.
This was odd to me, in that as a safety feature I think there are a lot of possible faults that could make it go open circuit, and this is the condition in which it thinks there is a basket. Sure, it could fail closed, but there are a lot more possibilities for it to fail open. Connector falls off, wire gets cut, switch moves in its mount, etc, etc. Of course it does make it easy if you don't want that feature, if you want to mow without the basket for example. In that case you could just remove one of the wires from the switch and it would think the basket was there. Handy if you want to bypass a safety feature, but not a very reliable approach I think. Am I missing something?
Anyway, I cleared a lot of debris away, cleaned the contacts, put it back, and it still didn't work. I then started to examine the mechanics of the operating mechanism, and soon saw that bottom of the basket clamps were not going fully down to the bottom of their slots. They were being obstructed by a right angle flange at the bottom of the back plate, as though the basket was there. When I checked at the back of that plate, where the switch is, I could see that the plunger was not very depressed, so it was still open, basket present and down state, hence why it still ran with the pto engaged.
I then looked at the right angle flange and could see that it had had a good number of bangs, and it was bent up under the left hand of the two basket clamps, which is where the switch is behind. Either one being held up would cause both to be up, because they are joined together. Anyway, I took a big pair of pliers, and bent that angle at the bottom of the back plate down and away from the clamp. This allowed it to drop down some more, and my multimeter confirmed that the switch had now gone closed, and visual examination showed that the operating plate on the back of that clamp had now depressed the plunger much further, closing the switch, which the multimeter had already confirmed. I then reconnected it and tried the pto again with the engine running, and the engine cut out. I then went back and bent it a little more to allow them both to fully bottom out with a clearance gap of about 1mm from the angled plate, and called it good, refitted the basket and tested properly. Normal operation is restored.
Switch view 1.jpg
Switch view 2.jpg
LH basket clamp and obstructing flange.jpg
Switch from above.jpg
Switch with operating paddle almost home 1.jpg
Thanks all.
Cheers
Sutty