we call them Piggy-back you lot call them shift starters , potatoes / potartoes
So as we have 2 mowers with similar problems I will be lazy & do some cut & paste
From this thread which you might like to keep an eye on
Troy bilt Broncho with a Kohler 5400 19HP. I was mowing my field and it just stopped as though it was out of gas. It had gas, I turned the key, nothing. Just quiet. I tried jumping it from my truck, ( I’ve done that before.). Still nothing. Spark plug is attached properly. Any suggestions...
www.lawnmowerforum.com
After checking the fuse, and by checking I mean pull it out and look
The next step is to try & turn the engine over by hand
Place your palm on the debris screen and push down while turning clockwise
Do 2 full revolutions
If you can not then remove the spark plug & try again.
If you can turn the engine 2 full revolutions by hand then get some jumper leads
Hook one to the battery - and the other directly to a metal part on the engine then turn the key.
Engine cranks = bad battery ground cable
Do the similar with the battery + terminal to the + terminal on the starter motor
Engine spins = bad power cable
And I have to ask, you did reset the blade switch didn't you ?
although from your description the blades should have been turned off
We have al been there wondering why an engine will not crank only to find we have left the blade switch turned on .
If the fuse is good and you have power to the key switch then when your turn the key the carburettor solenoid should energise with a faint click
AFAIK no mower runs the carb solenoid through any other switch than the key switch
Also if it lost power then the engine would stop but that alone would not stop the engine from cranking, unless the wires to it got shorted which of course would blow the main fuse .
PTO & brake switches like to ones you describe are usually found on mowers with a kill relay rather than directly grounding the magneto through the key switch
And of course they could also use the same relay to tigger the starter motor solenoid
Like JD Kubota are quite fond of throwing relays in all over the place .
How did that saying go ?
Nothing so simple works so well that it can not be made better by making it more complicated and thus less reliable .