Relay Usage
ECU/PTO*
Engine Control Unit/Power
Take-Off *Diesel 7.8 DURAMAX
®
BRK LAMP
C4/C5 Brake Lamps,
C6/C7/C8 Tractor/Trailer Wiring
DRL Daytime Running Lamps
IGN-4 Ignition
CHMSL Center High Mounted Stoplamp
MRK LTS Sidemarker and Clearance Lamps
HTD/MIRR Heated Mirrors
HTR Diesel Heated Fuel
RT TRN TRLR Passenger’s Side Trailer Turn Signal
Blank Not Used
LT TRN TRLR Driver’s Side Trailer Turn Signal
Blank Not Used
Blank Not Used
Blank Not Used
Underhood Fuse Block
When a circuit goes out, the problem could be in
either the primary or secondary underhood
fuse blocks. These blocks use blade-type fuses.
Both underhood fuse blocks are located in
the engine compartment, on the passenger’s side
of the vehicle.
To access the fuse blocks, gently squeeze both
sides of the cover to unlatch the tabs at the
top. Then, unsnap both attachments at the bottom
and remove the cover.
Be sure to replace fuses with fuses of the same
rating. Do not use fuses of higher amperage
than those indicated on the fuse block.
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