Which wires give constant, ignition and ground on a 2026 Chevrolet Low Cab Forward 3500HG-5500XG Gas?
On a 2026 Chevrolet Low Cab Forward 3500HG-5500XG Gas, take constant power from the Red wire at the rear manufacture connector J-118, center rear of the last crossmember, pin B, and ground to the Black wire at the rear manufacture connector J-118, center rear of the last crossmember, pin D. 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 sideCab power plug:B-220, left of the columnSystem voltage:12VEngine:6.6L gas
Where do I get constant, ignition and ground on a 2026 Chevrolet Low Cab Forward 3500HG-5500XG Gas?
GM gives the gas LCF an auxiliary power plug under the dash and a 4-pin body builder plug at the back of the frame.
Option 1 In the cab
Auxiliary power plug B-220
White 1-pin plug on the left side of the dash, left of the steering column.
Power
Light Green
Auxiliary power source plug B-220, left of the steering column, pin 1Fused supply from fuse F-41. GM does not say if it is live with the key off. Meter it before you use it as ignition or constant.
Ground
Black
End-of-frame connector H-66 (chassis harness to rear lamp harness), pin 7Ground to splice 1 (J-9 ground). In the cab, use clean bare metal.
GM does not print an ignition wire color for the cab on this truck. Meter B-220 key off and key on.
Option 2 Body and rear devices
Rear manufacture plug J-118
Black 4-pin plug, center rear of the last crossmember.
Constant
Red
Rear manufacture connector J-118, center rear of the last crossmember, pin BBattery voltage from fuse F-36.
Ground
Black
Rear manufacture connector J-118, center rear of the last crossmember, pin DGround.
Marker
Light Green/Black
Rear manufacture connector J-118, center rear of the last crossmember, pin AMarker lamp voltage.
Pin C (White/Black) is the rear dome lamp relay output.
All colors from GM's 2026 Chevrolet Low Cab Forward body builder electrical guide (gas section), printed as text in its connector tables.
Where are the turn signal, reverse and light wires on a 2026 Chevrolet Low Cab Forward 3500HG-5500XG Gas for advanced 360 multicam and video telematics installs?
Circuit
Wire color
Location and what it does
Left turnPositive +Not yet checked
Green/Black
End-of-frame connector H-66 (chassis harness to rear lamp harness), pin 1Left turn signal voltage.
Right turnPositive +Not yet checked
Green/White
End-of-frame connector H-66 (chassis harness to rear lamp harness), pin 8Right turn signal voltage.
Park lightPositive +Not yet checked
Green/Red
End-of-frame connector H-66 (chassis harness to rear lamp harness), pin 5Tail lamp voltage from fuse F-27.
HeadlightNot foundNot yet checked
Not found
Not foundNot printed in GM's guide.
ReversePositive +Not yet checked
Red/Blue
End-of-frame connector H-66 (chassis harness to rear lamp harness), pin 6Voltage only in reverse, fuse F-18. Same circuit at J-111 pin B.
BrakePolarity: meter itNot yet checked
Green
End-of-frame connector H-66 (chassis harness to rear lamp harness), pin 2GM calls it rear combination lights voltage. GM's older LCF manuals name Green as the stop lamp. Meter it.
Each chip shows the main insulation color with its stripe. Source: GM's 2026 Chevrolet Low Cab Forward body builder electrical guide (gas section).
Where are the brake, door, speed and CAN wires on a 2026 Chevrolet Low Cab Forward 3500HG-5500XG Gas 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, center rear of the last crossmember, pin BBattery voltage from fuse F-36.
Rear markerPositive +Not yet checked
Light Green/Black
Rear manufacture connector J-118, center rear of the last crossmember, pin AMarker lamp voltage, for body lamps.
Rear dome relayPositive +Not yet checked
White/Black
Rear manufacture connector J-118, center rear of the last crossmember, pin CRear dome lamp relay switched output.
Rear groundNegative -Not yet checked
Black
Rear manufacture connector J-118, center rear of the last crossmember, pin DGround. Also Black at H-66 pin 7 and J-111 pin A.
Back-up alarmPositive +Not yet checked
Red/Blue
Back-up alarm connector J-111, left frame rail ahead of the last crossmember, pin BVoltage only in reverse.
DoorsNot foundNot yet checked
Not found
Not foundNot printed in GM's guide.
Vehicle speedNot foundNot yet checked
Not found
Not foundNot printed in GM's guide.
Source: GM's 2026 Chevrolet Low Cab Forward body builder electrical guide (gas section). Headlight, door and speed wires are not printed there.
Where are the fuse boxes and ground points on a 2026 Chevrolet Low Cab Forward 3500HG-5500XG Gas?
Ground pointsJ-9 ground spliceRear lamp grounds run to J-9. In the cab, use clean bare metal, never the battery negative post.
From GM's 2026 Chevrolet Low Cab Forward body builder electrical guide (gas section). Our team has not yet checked these on a truck.
Where is the OBD-II port on a 2026 Chevrolet Low Cab Forward 3500HG-5500XG Gas?
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 2026 Chevrolet Low Cab Forward 3500HG-5500XG Gas?
This page2026Chevrolet LCF 3500HG, 4500HG, 5500HG, 5500XG gas.
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 2026 Chevrolet Low Cab Forward 3500HG, 4500HG, 5500HG and 5500XG with the 6.6L gas engine.
Every color here comes from GM's own 2026 body builder guide. Our own team has not yet metered these on a 2026 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 2026 Chevrolet Low Cab Forward 3500HG-5500XG Gas wiring
What wire is constant power on a 2026 Chevrolet Low Cab Forward 3500HG-5500XG Gas?
Red at the rear manufacture connector J-118, center rear of the last crossmember, pin B. Battery voltage from fuse F-36. Meter it before you tap it.
Where is the reverse wire on a 2026 Chevrolet Low Cab Forward 3500HG-5500XG Gas?
Red/Blue (positive +) at the end-of-frame connector H-66 (chassis harness to rear lamp harness), pin 6. Voltage only in reverse, fuse F-18. Meter it before you tap it.
Where is the brake wire on a 2026 Chevrolet Low Cab Forward 3500HG-5500XG Gas?
Green at the end-of-frame connector H-66 (chassis harness to rear lamp harness), pin 2. GM calls it rear combination lights voltage. Meter it before you tap it.
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