Which wires give constant, ignition and ground on a 2018 Chevrolet Low Cab Forward 4500HD-5500XD?
On a 2018 Chevrolet Low Cab Forward 4500HD-5500XD, take constant power from the Red wire at the FMS CAN interface connector H234 (white 6-pin), behind the center dash, pin 1, ignition from the Gray/Yellow wire at the FMS CAN interface connector H234 (white 6-pin), behind the center dash, pin 2, and ground to the Black wire at the FMS CAN interface connector H234 (white 6-pin), behind the center dash, pin 4. Meter every wire first.
Meter every wire before you tap it. Colors change with trim and build date.
OBD-II port:Under the dash, driver sideBest power spot:FMS CAN plug H234System voltage:12VEngine:Diesel
Where do I get constant, ignition and ground on a 2018 Chevrolet Low Cab Forward 4500HD-5500XD?
The 2018 diesel LCF has a factory FMS CAN interface plug made for telematics. GM prints battery, ignition, ground and CAN on it.
Option 1 Made for telematics
FMS CAN interface plug H234
White 6-pin plug at the FMS CAN interface unit, behind the center of the dash to the right of the radio (GM's locator drawing).
Constant
Red
FMS CAN interface connector H234 (white 6-pin), behind the center dash, pin 1Battery voltage.
Ignition
Gray/Yellow
FMS CAN interface connector H234 (white 6-pin), behind the center dash, pin 2Ignition voltage.
Ground
Black
FMS CAN interface connector H234 (white 6-pin), behind the center dash, pin 4Ground.
CAN 2
Brown/White (high)
Brown (low)
FMS CAN interface connector H234 (white 6-pin), behind the center dash, pins 6 and 5Read-only CAN for fleet devices.
Pin 3 is not used. Fuse any new feed close to the tap.
Option 2 Tracker only
At the OBD port
The wires on the back of the diagnostic connector.
Constant
Blue
OBD port (data link connector B-31), pin 16Battery voltage. Fine for a plug-in tracker.
Ignition
Not on this plug
Use Option 1The OBD port has no ignition pin.
Ground
Gray
OBD port (data link connector B-31), pins 4 and 5Ground. Gray, not black, on this truck.
CAN high is Green/White (pin 6), CAN low is Green (pin 14), K-line is Brown (pin 7).
All colors from GM's 2018 4500HD/4500XD/5500HD/5500XD Low Cab Forward electrical body builders manual, printed as text in its connector end views.
Where are the turn signal, reverse and light wires on a 2018 Chevrolet Low Cab Forward 4500HD-5500XD for advanced 360 multicam and video telematics installs?
End-of-frame connector H-66 (chassis harness to rear lamp harness), pin 5License plate and tail lamp feed.
HeadlightNot foundNot yet checked
Not found
Not foundNot read from GM's tables.
ReversePositive +Not yet checked
Red/Blue
End-of-frame connector H-66 (chassis harness to rear lamp harness), pin 6Backup lamps and back-up buzzer.
BrakePolarity: meter itNot yet checked
Green
End-of-frame connector H-66 (chassis harness to rear lamp harness), pin 2GM's 2018 table only says rear combination lights (both sides). GM's 6500XD manual names Green as the stop lamp. Meter it before you use it.
Each chip shows the main insulation color with its stripe. Source: GM's 2018 4500HD/4500XD/5500HD/5500XD Low Cab Forward electrical body builders manual.
Where are the brake, door, speed and CAN wires on a 2018 Chevrolet Low Cab Forward 4500HD-5500XD for advanced 360 multicam and video telematics installs?
Circuit
Wire color
Location and what it does
Rear battery feedPositive +Not yet checked
Red
Rear manufacture connector J-118, end of frameBattery voltage from the rear dome light fuse (15A).
Rear marker relayPositive +Not yet checked
Light Green/Black
Rear manufacture connector J-118, end of frameSwitched output from the marker lamp relay, for body lamps.
Rear dome relayPositive +Not yet checked
White/Black
Rear manufacture connector J-118, end of frameSwitched output from the rear dome lamp relay.
Rear groundNegative -Not yet checked
Black
End-of-frame connector H-66 (chassis harness to rear lamp harness), pin 7Ground for the rear lamps.
Ignition (Mimamori)Positive +Not yet checked
Violet
Mimamori telematics ECU plug B402, pin 1Ignition voltage at the factory Isuzu telematics unit.
Driver doorNegative -Not yet checked
Gray
Instrument panel inline connector H-85Door switch (LH) to the cluster.
Not foundSpeed travels on the CAN bus on this truck.
CAN busDataNot yet checked
Green/White (high)
Green (low)
OBD port (data link connector B-31), pins 6 and 14GM LAN. Never cut or splice these wires.
Source: GM's 2018 4500HD/4500XD/5500HD/5500XD Low Cab Forward electrical body builders manual (OEM connector end views). Headlight wire was not read.
Where are the fuse boxes and ground points on a 2018 Chevrolet Low Cab Forward 4500HD-5500XD?
Cab fuse and relay centerUnder the dashThe OBD battery and FMS feeds come from the cab fuse block.
Rear feedsRear dome fuse 15AFeeds the Red wire at J-118.
Ground pointsFMS pin 4 or OBD pins 4 and 5Or clean bare cab metal. Never the battery negative post.
From GM's 2018 4500HD/4500XD/5500HD/5500XD Low Cab Forward electrical body builders manual. Our team has not yet checked these on a truck.
Where is the OBD-II port on a 2018 Chevrolet Low Cab Forward 4500HD-5500XD?
OBD II
Diagnostic portOBD-II port: under the dash, driver sidePlug-in GPS trackers and OBD harnesses connect here. Check the port before you plan the install.
Which years share wiring with the 2018 Chevrolet Low Cab Forward 4500HD-5500XD?
This page2018Chevrolet LCF 4500HD, 4500XD, 5500HD, 5500XD diesel.
Help build this pageWant to be famous?Share a wire color, a photo or a tip for this truck, and your name goes on this page.
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This page covers the 2018 Chevrolet Low Cab Forward 4500HD, 4500XD, 5500HD and 5500XD diesel trucks, the Class 4 and 5 cab-overs built with Isuzu.
Every color here comes from GM's own 2018 body builders manual, which prints each connector pin as text. Our own team has not yet metered these on a 2018 truck.
Written by API Signal, fleet GPS and camera installers for 35+ years across Georgia, South Carolina and North Carolina, installing every major telematics and camera brand. Every wire on this page lists its source.
Test every wire with a meter before you tap it
No wiring information is ever guaranteed. Colors and locations change with trim, options and build date, and the manufacturer can change them in the middle of a model year. We share this as a starting point for installers, and you are responsible for confirming every connection on the truck in front of you.
Common questions about 2018 Chevrolet Low Cab Forward 4500HD-5500XD wiring
What wire is constant power on a 2018 Chevrolet Low Cab Forward 4500HD-5500XD?
Red at the FMS CAN interface connector H234 (white 6-pin), behind the center dash, pin 1. Battery voltage. Meter it before you tap it.
What wire is ignition on a 2018 Chevrolet Low Cab Forward 4500HD-5500XD?
Gray/Yellow at the FMS CAN interface connector H234 (white 6-pin), behind the center dash, pin 2. Ignition voltage. Meter it before you tap it.
Where is the reverse wire on a 2018 Chevrolet Low Cab Forward 4500HD-5500XD?
Red/Blue (positive +) at the end-of-frame connector H-66 (chassis harness to rear lamp harness), pin 6. Backup lamps and back-up buzzer. Meter it before you tap it.
Where is the brake wire on a 2018 Chevrolet Low Cab Forward 4500HD-5500XD?
Green at the end-of-frame connector H-66 (chassis harness to rear lamp harness), pin 2. GM's 2018 table only says rear combination lights (both sides). Meter it before you tap it.
Where is the parking brake wire on a 2018 Chevrolet Low Cab Forward 4500HD-5500XD?
White/Black (negative -) at the instrument panel inline connector H-85. Parking brake switch. Meter it before you tap it.
Where is the CAN bus on a 2018 Chevrolet Low Cab Forward 4500HD-5500XD?
Green/White (high) and Green (low) at the OBD port (data link connector B-31), pins 6 and 14. GM LAN.
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