Mower wiring 101
Cranking Circuit
Power usually goes from the hot side of the starter solenoid .
1) through a fuse
2) the the B ( = battery) terminal on the ignition switch ( tiny numbers under the switch )
3) to S (= Start) terminal on the switch
4) the the PTO switch or PTO safety switch on manual PTO's
5) to the brake safety switch
6) to the trigger wire on the solenoid.
This is a daisy chain so a break anywhere = no cranking
If the solenoid has only 1 small wire then the ground is via the case which will benefit from a clean where it contacts the body of the mower to get a good contact.
The ignition control can either be on the key switch
M + G = off
or on the throttle plate.
follow the thin wire from the coil
This is a ground wire.
Ground = off
Open circuit = on
Except on some ZTR's the seat switch is not in the cranking circuit.
Your problem is the ACR.
Your inlet valve should open just before TDC exhaust stroke then remain open all the way to BDC then close as the piston starts to rise.
Just before TDC the inlet should open a very small amount then close again .
Put your finger on the rocker or pushrod, you should feel them go tight then slack again as the ACR kicks in and drops out.
This is SOP for checking the cranking circuit
Before you start, pull the spark plug & try to rotate the engine by hand.
No use checking the electrics if you have a hydraulic lock, seized engine or jambed belt overloading the stater motor.
Assuming the engine turns freely.
I like to start from the starter motor and go backwards .
Do the following 5 tests, regardless of the results from an or all of them as there can be more than one problem and you want to isolate where the problem lies.
Elimination of individual parts is important so you know by the end, the battery, solenoid & heavy power circuits are all in good order.
1) try to jump the starter motor directly from your car or truck.
+ on the starter first then - to a good ground near the starter ( drain plug of lift hook are good )
Starter turns = starter good
2) do the same directly from the mowers battery
Starter turns = mower battery good
No turn = duff battery, recharge it & try again.
3) check for voltage ( + 12V ) at the solenoid trigger wire with the key in start position
3a) same with ground trigger wire ( 4 wire solenoid ) or body of solenoid ( 3 wire solenoid)
( I like to test V from the battery hot terminal to ground terminal rather than ohms as they give funny readings )
4) leave ground jumper in place ( from step 2 ) & try key start.
Starter turns = power connection good but ground connection suspect ( most common )
Confirm it by trying again, extra ground removed
5) Remove the trigger ( thin ) wire / wires from the solenoid.
Ground one on a 4 wire solenoid & bridge from the hot terminal to the other.
Starter cranks = solenoid good.
Solenoid is not polarity sensitive, BUT THE WIRING IS so make sure you remove the thin control wires.
Note a thinner wire on the hot terminal is not a control wire. It is the main power feed to the mower.
From here on things become very mower dependant as starting circuits are getting changed all the time.
Basically the power goes in a loop from the hot side of the solenoid ( saves wire, no other reason ) through the fuse to the B terminal on the key switch then to the PTO switch then to the parking brake switch then to the solenoid trigger switch , easy peasy after you grow the 3rd arm. Use a test lamp and follow the power.
However a lot of mowers with a 4 pole solenoid, run a secondary ground control circuit to the ground solenoid wire through the lap bars.
Then to stop this interfearing with the normal safety function of the ground kill, it goes to a relay with the ground as the switched connection.
These are a PIA as the + control wire to the relay comes from the power loop above and the ground side of the control comes via the normal cut out functions of the lap bars.
Be very careful because if you have a system like this and accidentally send 12V down the ground loop you can fry the magnetos on some circuits.nd from the grounding bolt to one of the starter mounting bolts & paint over both with liquid electrical tape.
