Hello Glen and AT
Stigas sold here from about 1979, when Rover introduced the clever
articulated Park 2000 Machine.
It is true that these machines abound with safety interlock switches,
and there is a big sound difference between an engine 'dying' under
load (like blade engagement) and dying because of ignition cut-out.
As aussietrev has said, it is an easy process to isolate a defective switch.
I presume the switch in question will be on the blade engagement lever.
I do feel though that we will need some photos (and model number)
to help further.
Hope this helps.
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Jack