Unfortunately MTD do not do printed manuals so this is the best I can do for a wiring diagram
Jacks MTS parts breakdown
Right click , pray to Allah , whatever Windoze users have to do to open the diagram in a new window / tab
Then print it out as big as your printer can make it.
Then go back to the original window, find the name for the various components and name them on the diagram.
I will hazard a guess that the DPO saw the black wire from the Ammeter to the fuse & mistook it for a ground wire .
On this model MTD have used GREEN for the Earth ( ground) wires which was actually not all that uncommon in the 70's & 80's .
Very Very important
Pull the ground ( kill ) wire off the magneto before doing anything because if it sees battery voltage let alone gets connected to it you will fry the timing chip.
Looks like the yellow wires, solid or two tone are the safety switch wires so ultimately should connect the magneto to ground to shut down the engine
The orange ( solid & two tone ) wires look like they are the starter solenoid safety wires which eventually put battery voltage to the starter solenoid when all of the switches are in the correct ( safe ) position to allow the engine to start.
The brake switch can be behind the dash or under the floor .