SECTION 06: ELECTRICAL
8
DOB 2490-2789 | X3-45 Commuter PA1605 Maintenance Manual (Final Version) – Sec 06 revised June 2017
VI = Volts Indirect. Electrical power is supplied
via master relay R1 which engages when
ignition key is in the ON or ACC position and
battery master switch (master cut-out) is set to
on.
Figure 2: Circuit Breaker Panel
06621
1.2 MULTIPLEX
FUSES
The multiplex outputs are protected in current by
an internal “soft-fuse”. Each output has
programmed specific maximum amperage.
When an output is shorted, the current gets
above the limit and the soft-fuse intervenes to
turn the output off. The output stays off until the
"soft-fuse" is reset.
Turn the ignition switch to the off position and
turn to the on position again. This resets all
"soft-fuses".
There is also hardware fuses used to protect the
incoming power to the multiplex modules. These
fuses are located inside the VECF (vehicle
electrical center front) and VECR (vehicle
electrical center rear).
1.3 RELAYS
Relays are used to automatically energize or de-
energize a circuit from a remote location. The
relay draws a very low current to energize its
coil. Once the coil is energized, it develops a
magnetic field that pulls a switch arm closed or
open, to either energize or de-energize a given
component. As the control current required for
the coil is very low, the relay allows a remote
station to control a high energy circuit without
running great lengths of costly high capacity
cable, and also eliminates the need for high
amperage switches and heavy connectors.
NOTE
Each relay is identified with “12v” or “24v”
printed on its casing in order to identify the
coil operating voltage.
CAUTION
The multiplex vehicle uses a VF4 relay
designed specifically for Volvo that has
different internal characteristics than the
current VF4 relay. It is important to use only
the new part marked Volvo as a replacement
in multiplex vehicles. Regular relays have an
inadequate lifespan for multiplex vehicles.
1.4 PRECAUTIONS
DANGER
Prior to working on a system inside vehicle,
make sure to cut electrical power and air
supply. A component could be supplied with
electricity even if the ignition switch is set to
the off position and/or a component could be
pressurized even if air tanks are emptied.
Always refer to the appropriate wiring and
pneumatic diagrams prior to working on
electrical and/or pneumatic systems.
CAUTION
Prior to arc welding on the vehicle, refer to
"multiplex modules disconnection procedure
prior to welding" in section 00 general of this
manual to avoid serious damage to the
vehicle components.
NOTE
When the ignition switch is set to the off
position, most electrical components are not
energized except for the fire suppression
system (AFSS). MCM (master chassis
module), ECM (engine control module), TCM
(transmission control module) and specific
multiplex modules will stay energized for a
period of 5 minutes after the ignition switch has
