MTD 700 Series Professional Shop Manual page 103

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Yellow/white wire
• Behavior: When the female pin terminal leading into the main harness is probed (yellow wire), there
should be continuity to ground only when the parking brake is on.
• Circuitry: The yellow wire with white trace leads to the parking brake switch, where it finds a path to
ground when the parking brake is on.
• Interpretation: If behavior is correct, the parking brake circuit is good. If there is continuity to ground
when the parking brake is off, the switch may be inoperative, or there may be a short to ground in the wire
leading to it. If there is not continuity to ground when the parking brake is on, the switch may be inopera-
tive or there may be an open condition in the wire leading to it.
Red wire with black trace
• Behavior: There is a red wire with black trace between yellow wire with a black trace and the green wire.
This wire provides the module with input from the reverse switch. When the mower is in reverse, this ter-
minal should have continuity to ground.
• Circuitry: This wire runs directly to the reverse safety switch. This is a simple metal tang switch that
grounds-out against the shift/speed lever.
• Interpretation: Continuity to ground when the mower is not in reverse would indicate a short to ground.
This could take the form of a chafed wire contacting ground, a bent reverse safety switch that is always in
contact with another metal part, or a broken plastic insulator that separates the switch from the frame or
fender depending on the transmission.
Lack of continuity to ground would indicate a broken or disconnected wire leading to the reverse safety
switch, or a switch that is not closing because of physical damage or corrosion.
Green wire(s)
• Behavior: At the opposite end of the top row from the yellow wire with black trace is a green wire. The
green wire should always have continuity to ground.
• Circuitry: The green wire(s) leads to ground.
• Interpretation: If this ground path is not good, there will probably be other ground-related issues with the
mower: slow starter motor, slow battery charge, dim lights. All ground connections should be mechanically
secure and corrosion free.
Red wire
• Behavior: The red wire on the OCR plug carries battery voltage. It should show D.C. battery voltage
when the key switch is in any of the run positions.
• Circuitry: This wire draws power directly from the A1 terminal on the key switch.
• Interpretation: If there is no battery voltage at this terminal, the mower is probably not functioning at all.
Look for a blown fuse, disconnected battery or some other major fault.
White wire
• Behavior: There should be continuity to ground at this terminal when the key switch is in the REVERSE
CAUTION MODE position.
• Circuitry: When the key switch is in the REVERSE CAUTION MODE position, a ground path is estab-
lished by connecting terminal A2 to terminal L within the key switch. The purple wire from the OCR mod-
ule connects to A2, and a green ground wire connects to L.
• Interpretation: If the purple wire fails to reach a ground path when the key switch is in the REVERSE
CAUTION MODE position, the OCR module will not arm or operate. Check the key switch for continuity
between A2 and L in the REVERSE CAUTION MODE position, confirm that the green wire connecting to
the L terminal does have good continuity to ground, and check for any loss of continuity in the white wire
that extends from the key switch to the OCR module, including the molded connector between the two
components.
4. If the OCR plug test indicates fault with any of the safety switches, the next step is to test the suspect switch.
The operation of those switches are described in the following sections.
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