Fault Code Guide
Introduction
Optional power switches are factory-installed, switch-
controlled power provisions that can be ordered for a
Business Class
®
M2 vehicle. Optional switches can
be ordered in a one-, two-, or four-switch configura-
tion. All optional switches mount on the dash, provide
fuse-protected battery power, and route to a cus-
tomer access point. Optional switches are commonly
used to provide battery-powered lighting, such as
dome, spot, or beacon lights. Other applications in-
clude using the optional switch as a triggering
mechanism to enable other features, such as hydrau-
lic lift operations or access panel locks.
Overview
Available optional switch configurations include:
• one switch with a customer-access junction
block
• one switch with a blunt-cut output
• two switches with blunt-cut outputs
• four switches with blunt-cut outputs
Optional power switches are mounted on the dash to
the right of the steering column. Each switch is
equipped with two LED lights; one LED provides
switch illumination while the other indicates when the
switch is in the on position. Battery-powered power
distribution module (PDM) fuses, located under the
hood, provide a constant power feed to each switch.
When a switch is turned to the on position, the
switch contacts close and supply battery power to an
output circuit.
For vehicles with a single optional switch and junc-
tion block configuration, the output circuit from the
optional switch is a red wire that connects to the
5-post junction block. The junction block is usually
located on the frame rail near the Chassis Module
(CHM) and provides a connection point that permits
easy access. The red wire in the junction block is
connected to the 15-amp optional switch output,
while the yellow wire is connected to a marker light
feed from the CHM. See Section 54.35 for informa-
tion on the junction block marker light feed.
For all other optional switch configurations, the out-
put circuits from the optional switches route along the
chassis toward the back of the cab where the circuits
terminate inside the left frame rail near the standard
location of the CHM on a vehicle with a day cab. On
a vehicle with an extended cab or a crew cab, the
circuits terminate under the cab.
Output circuits terminate as blunt-cut ends sealed in
heat shrink. The blunt-cut ends extend a few inches
out from the harness loom and are individually
tagged with an identification label. The label identifies
which switch is powering the circuit and also the cur-
rent capacity of the circuit. See Fig. 1.
Current Capacity
It is important to note that the current capacities for
optional switch outputs are not the same for all con-
figurations. Current capacities differ according to the
number of switches that come installed on a vehicle.
For instance, for a two-switch configuration, the
fused battery feed for both switches is supplied by
one PDM fuse. This means that the total combined
load from both switches cannot exceed the fuse rat-
ing. For optional-switch current capacities, see
Table 1.
Optional-Switch Current Capacity
No. of
Switches
PDM Fuse F25 PDM Fuse F26
Switch Output
Current Capacity
Rating Switch Protected Rating Switch Protected
1 15A Switch 1 — — 15A
12/21/2005 f544744
Fig. 1, Blunt-cut End
Optional Power Switches and Connection
54.39
General Information
Business Class M2 Workshop Manual, Supplement 10, September 2006 050/1