If you would like to tell us which particular mower you have you will get better advice.
1) find the plug for the clutch in the engine bay and test it for 12V when the clutch is turned on.
On some mowers you need to be in the seat for the switch to activate and some you don't but we dont know so so for now put a bum of some sort on the seat to do the test.
Check for 12 V between the 2 wires and 12 V between the + wire & the ground and for continuity between the ground wire & the mower chassis.
2) do the same tests at the switch
Check you have good fuses.
Some mowers run a fuse for the clutch and a fuse for the mower, others don't.
And then of course it could be a relay because some use a relay to power the clutch and some don't.
