The brake switch, or rather the parking brake switch is directly behind the parking brake lever
It has 4 wires, a yellow a yellow & 2 violets
Looks like exmark have drawn the schmetic wrong so check the switch first .
Looks like brake off the yellow & violets are connected and grey is disconnected
So with the brake on the grey & violet is connected & the yellow might be disconnected, or the grey , yellow & violet might all be connected
With all ZTR's I use a few short jumper wires to manually make the connections that each switch would normally make.
This gets done one switch at a time till the problem goes away and the last switch jumped was obviously the faulty one.
Using a multi meter can give a false OK because a terminal that is just barely touching will show continuity but will not carry voltage.