Guardian 4270 Diagnostic Repair Manual page 21

Section 5
ENGINE DC CONTROL SYSTEM
CIRCUIT CONDITION- PRE-HEAT:
When the PRE-HEAT SWITCH (SW) or the
REMOTE PANEL PRE-HEAT SWITCH is closed by
the operator, battery voltage is delivered across the
closed switch contacts to the PRE-HEAT CONTAC-
TOR (PHC) via Wire 150. The PRE-HEAT CONTAC-
TOR (PHC) is now energized. The normally open
(PHC) contacts close, battery voltage is now avail-
able to Wire 157.
The GLOW PLUGS (GP) are energized via Wire 157.
Wire 157 is also connected to a DIODE (D1), current
is allowed to pass through (D1) and Wire 14 will now
have battery voltage applied to it " Engine Controller
Terminals 9, 10 , and 11 are connected".
The FUEL PUMP (FP), FUEL SOLENOID (FS), and
HOURMETER (HM) will be energized via Wire 14.
Wire 14 is also connected to RESISTOR (R2) and
DIODE (D2). After passing through R2 and D2
reduced voltage is applied to Wire 4.
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