2021 Chevrolet Silverado 4500HD, 5500HD and 6500HD
Medium duty chassis cab. Duramax diesel.
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Which wires give constant, ignition and ground on a 2021 Chevrolet Silverado 4500HD, 5500HD and 6500HD?
On a 2021 Chevrolet Silverado 4500HD, 5500HD and 6500HD, take constant power from the Red/Dark Blue wire at the OBD port (data link connector X84), pin 16, circuit 3240, and ground to the Black wire at the OBD port (data link connector X84), pin 4, circuit 1050. Meter every wire first.
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.
This page covers the 2021 Chevrolet Silverado 4500HD, 5500HD and 6500HD medium duty chassis cabs.
Every color here comes from GM's own 2021 electrical body builder manual: the wires at the OBD port, the power outlets and the trailer connector. No ignition wire color was found, only an accessory wire and an uncolored run pin. Our own team has not yet metered these on a 2021 truck.
OBD-II portLocation not confirmed
Best power spotOBD port wires or the dash power outlets
System voltage12V
Ignition typeNot confirmed
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Where do I get constant, ignition and ground on a 2021 Chevrolet Silverado 4500HD, 5500HD and 6500HD?
GM prints a battery feed and a ground at the OBD port, and battery and accessory feeds at the power outlets. No ignition wire color was found.
Option 1 Constant and ground
At the OBD port
The wires on the back of the 16-pin diagnostic connector.
Constant
Red/Dark Blue
OBD port (data link connector X84), pin 16, circuit 3240Fused battery feed to the OBD port. Thin wire, so use it for a tracker only.
Ignition
Not found
Not foundNo ignition wire color was found. See the accessory wire in option 2 and the run pin listed further down.
Ground
Black
OBD port (data link connector X84), pin 4, circuit 1050Ground. Pin 5 is a second ground, Black/White.
From GM's 2021 electrical body builder manual for this truck. The manual puts this connector in the instrument panel harness. Its exact spot under the dash was not found.
Option 2 Constant, accessory, ground
Power outlets
Behind the dash and console power outlets, on trucks that have them.
Constant
Red/White (outlet 1)
Red/Brown (outlet 2)
Instrument panel power outlets X80J and X80K, pin A on eachFused battery feeds. Live at all times.
Accessory
Violet/Yellow
Rear center console power outlet X80L, pin A, circuit 243Accessory voltage. Follows the key and retained accessory power, so it can stay on for a while after the truck is shut off.
Ground
Black
Pin C on each outlet, circuit 1050Ground.
From GM's 2021 electrical body builder manual for this truck. These outlets come with option D07. Stay well under the outlet fuse rating.
All colors from GM's 2021 electrical body builder manual for this truck. GM also documents run, accessory, battery and ground pins at the junction block under the steering wheel, but prints no colors for them.
What are the turn signal, reverse and light wires on a 2021 Chevrolet Silverado 4500HD, 5500HD and 6500HD?
Circuit
Wire color
Location and what it does
Left turnPositive +Not yet checked
Yellow/Blue
Trailer connector X88, rear left of the chassis (trucks with trailer option UY7), pin GLeft stop and turn output for a trailer.
Right turnPositive +Not yet checked
Green/Brown
Trailer connector X88, rear left of the chassis (trucks with trailer option UY7), pin DRight stop and turn output for a trailer.
Park lightPositive +Not yet checked
Gray/Brown
Trailer connector X88, rear left of the chassis (trucks with trailer option UY7), pin FPark lamp output for a trailer.
HeadlightNot foundNot yet checked
Not found
Not foundWe found no source for this wire.
ReversePositive +Not yet checked
White/Green
Trailer connector X88, rear left of the chassis (trucks with trailer option UY7), pin ABackup lamp output for a trailer.
Dome lightNot foundNot yet checked
Not found
Not foundWe found no source for this wire.
Each chip shows the main insulation color with its stripe. Source: GM's 2021 electrical body builder manual for this truck (trailer connector X88).
Where are the brake, door, speed and CAN wires on a 2021 Chevrolet Silverado 4500HD, 5500HD and 6500HD?
Circuit
Wire color
Location and what it does
BrakePositive +Not yet checked
Yellow/Blue (left)
Green/Brown (right)
Trailer connector X88, rear left of the chassis (trucks with trailer option UY7), pins G and DStop is combined with the turn signal on these two wires. No separate brake wire was found.
Ignition (pin only)Positive +Not yet checked
Not found
Junction block X61A under the steering wheel, connector X7, pin 11, circuit 1939Run and crank voltage, 15 amp circuit. GM printed this pin in a 2019 bulletin with no wire color, and it is not confirmed for 2021. Pin 8 is accessory, pins 7 and 17 are battery, pin 10 is ground.
DoorsNot foundNot yet checked
Not found
Not foundWe found no source for this wire.
Parking brakeNot foundNot yet checked
Not found
Not foundGM bulletin 184 gives a park status signal at the body control module, but only after a lead is added and the module is reprogrammed.
HazardNot foundNot yet checked
Not found
Not foundWe found no source for this wire.
Trailer battery feedPositive +Not yet checked
Red/Violet
Trailer connector X88, rear left of the chassis (trucks with trailer option UY7), pin EGM says battery voltage is on this pin at all times. Pin B is a Black ground.
Upfitter switch outputsPositive +Not yet checked
Not found
Junction block X61A under the steering wheel, connector X7, pins 20, 14, 4 and 1 (trucks with upfitter switches, option 9L7)Outputs of dash switches 1 to 4, 30 amps each. GM printed these pins for 2019 with no wire colors.
Vehicle speedPolarity: meter itNot yet checked
Not found
Junction block X61A under the steering wheel, connector X7, cavity 19GM bulletin 182 gives this pin for 2021: 4,000 pulses per mile. No wire color is printed.
CAN busDataNot yet checked
Dark Blue (+)
White (-)
OBD port (data link connector X84), pins 6 and 14High speed GMLAN bus 1. A second high speed bus is on pins 12 (Dark Blue/Yellow) and 13 (White), and low speed GMLAN is on pin 1 (Light Green). Never cut or splice these wires.
Sources: GM's 2021 electrical body builder manual for this truck, GM upfitter bulletins 148e, 182 and 184, and GM TechLink. Doors, hazard, headlight and dome wires, the ignition type and the exact OBD port position were not found.
Which years share wiring with the 2021 Chevrolet Silverado 4500HD, 5500HD and 6500HD?
This page2021Silverado 4500HD, 5500HD and 6500HD.
Same wiringNone confirmedGM prints one electrical manual for 2019 and 2020, one for 2021, one for 2022 and one for 2023 and newer. Only the 2021 connector pages could be read.
Not this pageOther years, the International CV and the Silverado 2500HD and 3500HDThe International CV is built on the same line and uses the same connector names, but its wire colors are not confirmed. The 2500HD and 3500HD are different trucks.
Where are the fuse boxes and ground points on a 2021 Chevrolet Silverado 4500HD, 5500HD and 6500HD?
InteriorTwo instrument panel fuse blocks, left and rightGM names them X51L and X51R. The junction block with the upfitter pins is under the steering wheel.
Under the hood and cabUnderhood fuse block. Battery box under the cab, driver sideGM describes a covered jump start positive stud beneath the driver door on the 2019 truck.
Ground pointsBlack ground wires at each connectorNo named ground stud was found. Use clean, bare body metal if you add a ground.
No fuse list could be read for this truck, so no fuse tap position is given. GM moves a 5 amp fuse between two slots to switch the upfitter switches from battery to run power, and says never to fill both slots of a pair.
Where is the OBD-II port on a 2021 Chevrolet Silverado 4500HD, 5500HD and 6500HD?
OBD II
Diagnostic portOBD-II port: location not confirmedLook under the driver side dash first, and send us a photo if you find it.
Common questions about 2021 Chevrolet Silverado 4500HD, 5500HD and 6500HD wiring
What wire is constant power on a 2021 Chevrolet Silverado 4500HD, 5500HD and 6500HD?
Red/Dark Blue at the OBD port (data link connector X84), pin 16, circuit 3240. Fused battery feed to the OBD port. Meter it before you tap it.
Where is the reverse wire on a 2021 Chevrolet Silverado 4500HD, 5500HD and 6500HD?
White/Green (positive +) at the trailer connector X88, rear left of the chassis (trucks with trailer option UY7), pin A. Backup lamp output for a trailer. Meter it before you tap it.
Where is the brake wire on a 2021 Chevrolet Silverado 4500HD, 5500HD and 6500HD?
Yellow/Blue (left) and Green/Brown (right) (positive +) at the trailer connector X88, rear left of the chassis (trucks with trailer option UY7), pins G and D. Stop is combined with the turn signal on these two wires. Meter it before you tap it.
Where is the vehicle speed signal on a 2021 Chevrolet Silverado 4500HD, 5500HD and 6500HD?
The wire color is not published. It is at the junction block X61A under the steering wheel, connector X7, cavity 19. GM bulletin 182 gives this pin for 2021: 4,000 pulses per mile. Meter it before you tap it.
Where is the CAN bus on a 2021 Chevrolet Silverado 4500HD, 5500HD and 6500HD?
Dark Blue (+) and White (-) at the OBD port (data link connector X84), pins 6 and 14. High speed GMLAN bus 1.
Which years share wiring with the 2021 Chevrolet Silverado 4500HD, 5500HD and 6500HD?
None confirmed. GM prints one electrical manual for 2019 and 2020, one for 2021, one for 2022 and one for 2023 and newer.
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