5-4
Engine Coolant
Temperature (ECT)
Switch/Thermistor
The ECT switch/thermistor is a two-function device.
One side is a normally open, temperature activated
switch that closes when high coolant temperature is
detected activating the high temperature circuit in the
speedometer/LCD. The other side contains a tempera-
ture sensitive resistor (thermistor) that provides tem-
perature information to the glow plug controller/relay.
To test the ECT switch/thermistor, use the following
procedure.
1. Suspend the ECT switch/thermistor and a ther-
mometer in a container of cooking oil.
NOTE: Neither the ECT switch/thermistor nor the
thermometer should be allowed to touch the bot-
tom of the container or inaccurate readings will
occur. Use wire holders to suspend the ECT
switch/thermistor and thermometer.
2. Connect one meter lead to the base of the
switch/thermistor and the other meter lead to the
switch pin. With the meter in the OHMS position,
the meter should read an open circuit.
DE650A
3. Remove the meter lead from the switch pin and
connect to the thermistor pin; then heat the oil and
note the temperature and meter readings.
4. When the temperature reaches 20° C (68° F), the
meter should read 1k ohms.
5. When the temperature reaches 40° C (104° F), the
meter should read 460 ohms.
6. When the temperature reaches 50° C (122° F), the
meter should read 320 ohms.
7. Remove the meter lead from the thermistor pin
and connect to the switch pin; then continue to
heat the oil.
8. When the temperature reaches approximately 110°
C (230° F), the meter should read less than 1 ohm.
Glow Plug
Controller/Relay
The glow plug controller/relay is a plug-in device
located under the seat. The glow plug controller/relay
applies 12 DC volts to the glow plugs in the pre-com-
bustion chambers to aid in cold starting. Heating time
is determined by the ECT thermistor signal and will
vary from 0 seconds (warm engine) to approximately
30 seconds (cold engine).
NOTE: The glow plug controller/relay is not a ser-
viceable component. To test the controller/relay,
use the following procedure.
1. Using an appropriate multimeter, select DC Volts
and connect the black (-) tester lead to the black
(85) wire and the red (+) tester lead to the
red/orange (30) wire. The meter must read battery
voltage. If no battery voltage is present, check the
connection at the starter relay.
2. Connect the red tester lead to the white/blue (87)
wire and momentarily turn the ignition switch to
the ON position. The meter should read battery
voltage for up to 30 seconds; then drop to zero.
3. Connect the red tester lead to the yellow/orange
(L) wire and turn the ignition switch to the ON
position. The meter should read battery voltage
and the green glow plug indicator should illumi-
nate for up to 30 seconds.
4. Turn the ignition switch off.
5. Turn the ignition switch to the ON position.
Observe the glow plug indicator while momen-
tarily “bumping” the starter button. The glow plug
indicator should immediately extinguish.
6. If steps 2, 3, or 5 are not as specified, replace the
glow plug controller/relay.
7. If the glow plugs remain on for more than 35 sec-
onds, test the ECT switch/thermistor (thermistor
side only).
NOTE: To test the glow plugs, use the following
procedure.
1. Disconnect the white/blue glow plug power wire
from the right-side glow plug; then disconnect the
jumper wire running to the left-side glow plug.
! WARNING
Wear insulated gloves and safety glasses. Heated oil
can cause severe burns.
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