Defender Electric Diagrams. Manual - part 21

CIRCUIT OPERATION

DEFENDER 90 NAS

IGNITION AND SHIFT INTERLOCK

DESCRIPTION

Ignition interlock

The ignition interlock prevents the following actions unless the gear selector lever is in
the Park position and the transfer box is in either High or Low range:

•

Key cannot be turned from position 'I' to position '0'.

•

Key can be turned to crank position 'III' but starter motor will not operate.

Shift interlock

The shift interlock prevents the gear selector lever being moved from the Park position
unless the ignition key is in position 'II' and the foot brake is applied.

Transfer gearbox interlock

The transfer gearbox interlock prevents the transfer box selector lever being moved unless
the ignition switch is in position 'II' and the gear selector lever is in the Park or Neutral
position.

OPERATION

Feed from the positive battery terminal is connected to the engine compartment fuse box
(C632-1) by the brown wire. Current passes through fusible link 1 and fusible link 5 of
the engine compartment fuse box which are connected in series. Fusible link 5 (C570-2)
is connected to the ignition switch (C28-1) by the brown wire.

Ignition interlock

Fuse 2 of the engine compartment fuse box is connected in series with fusible link 1 of the
engine compartment fuse box. Fuse 2 (C574-3) is connected to the key in sensor (C672-
1) by the purple wire. Inserting the key in to the ignition switch closes the key in sensor
and allows power to flow from the key in sensor (C672-2) to the key interlock solenoid
(C671-1) and diode (C924-2) on the brown/red wire. The diode prevents back feeding as
the solenoid energizes and de-energizes.

With the transfer gearbox in neutral, the transfer gearbox neutral switch will be closed.
With the neutral switch closed, current flows through the winding of the key interlock
solenoid (C671-2) on the brown/yellow wire, through the diode (C802-2 & 3), through
the switch (C684-3) to ground on the black wire and the solenoid remains energized,
preventing the key being turned to position ‘0’ and, hence removed from the ignition.

CIRCUIT OPERATION

DEFENDER 90 NAS

Similarly, if the automatic transmission selector lever is not in park, the PARK 1 switch
will be closed and a ground path is provided for key interlock solenoid on the
brown/yellow wire, through the closed switch contacts, on the black wire (C668-4) &
(C550-6). Again, the key interlock solenoid will be energized an the key cannot be
removed.

Either, or both, of the above conditions will cause the key interlock solenoid to be
energized. Only with the transfer gearbox neutral switch open (in the HI or LO positions)
AND the automatic transmission selector lever in park, is the key interlock de-energized,
enabling the key to be moved to position ‘0’ and removed from the ignition.

Shift interlock

The ignition switch (C94-1) is connected to fuse 18 of the passenger compartment fuse
box (C581-13) by the white wire. With the ignition switch in position 'II', power flows
across fuse 18 (C581-14) to the brake pedal switch (C75-1) on the green/purple wire.
When the brake pedal is depressed, the switch closes and power flows across the switch
(C29-1) to the automatic transmission selector (C668-2) on the green/purple wire. An
internal link connection takes the feed out of the selector (C668-5) on a pink/slate wire,
and back to the PARK 2 switch (C668-6). If the gear selector is in the Park position, the
route to ground for the gear shift interlock solenoid (C668-3) is provided on the black
wire. With the gear shift interlock solenoid energized, the gear shift lever is released,
allowing the lever to be moved from the Park position. If the gear shift lever is not in the
Park position, the shift interlock solenoid has no continuity to ground and is not
energized. With the shift interlock solenoid de-energized, the gear selector lever cannot
be moved from the Park position. Similarly, if the brake pedal switch is not closed by
depressing the brake pedal, power is not supplied to the gear shift interlock solenoid,
regardless of the gear selector lever position.

Transfer gearbox interlock

Fuse 2 of the engine compartment fuse box is connected in series with fusible link 1 of the
engine compartment fuse box. Fuse 2 (C574-3) is connected to the key in sensor (C672-
1) by the purple wire. Inserting the key in to the ignition switch closes the key in sensor
and allows power to flow from the key in switch (C672-2) to the interlock relay winding
(C95-85) on the brown/red wire via a header joint (C289). If the automatic transmission
inhibitor switch is not in the neutral or park position, there is no ground path for the
interlock relay winding and the relay remains de-energized. In this condition, the transfer
gearbox selector lever cannot be moved.

CIRCUIT OPERATION

DEFENDER 90 NAS

With the automatic transmission inhibitor switch in either Park or Neutral, a ground path
is provided for the interlock relay winding (956-86), on the black/yellow wire, through the
diode (C801-1 & 2), through the closed switch contacts (C069- 5 & 4), to the
immobilization ECU on a black/orange wire (C057-10) and from the immobilization ECU
(C057-11) to ground on a black wire. With the relay energized, current flows from fuse
18 of the passenger compartment fuse box (C581-14) to the interlock relay (C956-87) on
a green wire. Current passes through the closed relay contacts (C956-30) to the transfer
gearbox interlock unit (C683-1) on the slate/black wire and to ground through the unit’s
solenoid winding on the black wire. In this condition, the unit is energized and the transfer
gearbox selector lever is free to move.

CONNECTOR DETAILS

DEFENDER 90 NAS

C1
DIRECTION
INDICATOR - LH
2 Way
Female
RED
Behind LH front indicator
lamp

Cav

Color Cct

ALL

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