MTD 700 Series Professional Shop Manual page 99

FOR DISCOUNT PARTS CALL 606-678-9623 OR 606-561-4983
Symptom: Crank, but no spark: This is a highly unlikely scenario. If it occurs after a key switch has been
changed independently of the OCR module, this would arouse suspicion that the wrong key switch was
installed. Otherwise, the problem lies elsewhere in the safety circuits or engine. Do not over look the pos-
sibility of a bad magneto or chafed ground lead within the engine harness.
In the NORMAL RUN position (green zone), the B and A1 (L on 5-pin switches) terminals should have continuity.
Symptom: Battery does not charge: Follow the engine manufacturer's recommendations for testing alterna-
tor output.
NOTE: A blown fuse will disable the starter and the charging circuits. A simple quick-test for the presence of
alternator output at the battery is to check across the battery posts for DC voltage.
Symptom: After fire solenoid does not work: engine starts and dies: The after fire solenoid is powered by
the red wire with a white trace from the A1 (L on 5-pin switches) terminal of the key switch, and should
operate independently of anything else on the mower once the engine is running. If the alternator fails
and battery power is not reaching the after fire solenoid through the key switch, it will not work. This is an
unusual set of circumstances.
In the REVERSE CAUTION MODE (yellow zone), the same characteristics are true as for the normal run position,
but in addition the L terminal will have continuity with the A2 terminal.
The A2 terminal is connected to the OCR module by a white wire. The L terminal (formerly used for the light-
ing circuit) connects directly to the ground circuit of green wires. When the key is in the REVERSE CAU-
TION MODE position, the white wire carries a ground signal to the OCR module. When the parking brake
is released, this ground signal arms (enables), but does not turn on the OCR module.
Symptom: OCR module will not turn on: Make sure the parking brake is released. Check for continuity
between A2 and L terminals on the key switch when it is in the REVERSE CAUTION MODE position.
Confirm that the green wire has continuity to ground. If the switch is capable of establishing a ground sig-
nal to the OCR module, the problem is likely to lie elsewhere in the system.
Symptom: OCR module will not turn on: confirm that the ground path (continuity to ground) to the white
wire is broken when the key switch is in any position other than REVERSE CAUTION MODE.
The OCR module is disarmed (disabled) when the parking brake is set. To re-arm the module, the key is
moved to another position, breaking the ground signal, then returned to the REVERSE CAUTION MODE,
re-establishing the ground signal. It works something like a latched relay. If it is not possible to break the
ground-path, it is not possible to freshly establish it either, and the OCR module will not be armable.
Causes for such a condition might include a shorted or incorrect key switch, or a chafed white wire shorting
to ground between the key switch and the OCR module.
www.mymowerparts.com
Electrical
93