Additional heater control unit
M75
is supplied at pin 1 (connector B) directly from the battery.
The earth is taken to pin 2 (connector B)
via additional heater relay
J36
, switch
I20
and relay
R1
of junction unit
B1
.
When relay
R1
is energised via the
line (INT/A) its contact supplies the coil of additional heater
relay
J36
via fuse
F13
. Control unit
M75
receives an earth signal via its contact.
Pin 3 of connector A of
M75
receives
a signal from the appropriate temperature sensor
K79
, which
measures air temperature within the engine bay.
The sensor only works with the engine running;
it receives a reference signal from alternator (D+); this signal
is low (earth) when the alternator is not turning. The signal becomes
high (12 V) and supplies the sensor when the engine is running.
Pin 6 of connector A controls additional
heater pump
N44
, which is earthed through inertia switch
I50
.
In case of impact, this cuts off the circuit to prevent the danger
of fuel emerging.
Control unit
M75
is equipped with
a self-diagnostic system that may be used by connecting the unit
to connector
R10
through pin 2 of connector A.