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Which wires give constant, ignition and ground on a 2015 Isuzu NPR-HD, NQR and NRR Diesel?
On a 2015 Isuzu NPR-HD, NQR and NRR Diesel, take constant power from the Red/Green wire at the trailer brake controller wires behind the radio (heavy gauge wire), and ground to the Black wire at the trailer brake controller wires behind the radio (thin gauge wire). 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 2015 Isuzu N-Series diesel trucks: NPR-HD, NQR and NRR.
This page is short. Every wire here comes from Isuzu's own 2015 body builder guide: a battery feed and ground behind the radio, and the lamp wires at the trailer, rear body and back up alarm plugs on the frame. No ignition wire was found, and nothing here has been checked against a gas truck. Our own team has not yet metered these on a 2015 truck.
OBD-II portLocation not confirmed
Best power spotBrake controller wires behind the radio
System voltage12V
Ignition typeNot confirmed
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Where do I get constant, ignition and ground on a 2015 Isuzu NPR-HD, NQR and NRR Diesel?
Isuzu gives a battery feed and a ground behind the radio. No ignition wire was found for this truck.
Option 1 Constant and ground
Behind the radio
The trailer brake controller pigtail. In the cab, close to where most devices mount.
Constant
Red/Green
Trailer brake controller wires behind the radio (heavy gauge wire)Battery feed for a brake controller, fused at 20 amps. It can be dead until the supply harness under the cab, behind the passenger side headlight, is connected. Meter it first.
Ignition
Not found
Not foundNo source gave an ignition wire or a key-switched fuse for a 2015 truck.
Ground
Black
Trailer brake controller wires behind the radio (thin gauge wire)Ground wire in the same pigtail. 10 amps maximum.
From Isuzu. Take out the radio and the pocket under it, then pull out the brake controller pigtail. There are two plain Red wires in it as well: the heavy one is the brake controller output and the thin one is a brake signal. Do not use either one for power.
Option 2 Body power
Rear body connector
Four-wire plug at the last crossmember for body equipment.
Body power
Red
Rear body connector J-118, center rear of the last crossmember, pin BIsuzu calls it power source voltage. The guide does not say if it is battery fed or key switched, so meter it with the key off and on.
Ground
Black
Rear body connector J-118, center rear of the last crossmember, pin DGround for rear body equipment.
From Isuzu. This plug is at the back of the frame, so it suits equipment mounted on the body. The same plug has the marker light and body dome light wires listed below.
All wires from Isuzu's 2015 body builder guide for the diesel N-Series. Isuzu lists the brake controller and trailer wiring as trailer provisions and does not say whether every truck has them.
What are the turn signal, reverse and light wires on a 2015 Isuzu NPR-HD, NQR and NRR Diesel?
Circuit
Wire color
Location and what it does
Left turnPositive +Not yet checked
Green/Black
Trailer connector H-172, left inner side of the frame rail, behind the transmission crossmember, pin 3Left turn signal output for a trailer.
Right turnPositive +Not yet checked
Green/White
Trailer connector H-172, left inner side of the frame rail, behind the transmission crossmember, pin 4Right turn signal output for a trailer.
Park lightPositive +Not yet checked
Green/Red (tail)
Light Green/Black (marker)
Trailer connector H-172, left inner side of the frame rail, behind the transmission crossmember, pin 2 for the tail lamps. Marker lights are on Rear body connector J-118, center rear of the last crossmember, pin ALive with the lights on.
HeadlightNot foundNot yet checked
Not found
Not foundWe found no source for this wire.
ReversePositive +Not yet checked
Red/Blue
Back up alarm connector J-111, left inner frame rail, behind the last crossmember, pin 1Back up alarm supply. Live in reverse. Pin 2 is a Black ground.
Dome lightPositive +Not yet checked
White/Black
Rear body connector J-118, center rear of the last crossmember, pin CFeed for a rear body dome light. This is not the cab dome lamp, and no cab dome wire was found.
Each chip shows the main insulation color with its stripe. Source: Isuzu's 2015 body builder guide for the diesel N-Series.
Where are the brake, door, speed and CAN wires on a 2015 Isuzu NPR-HD, NQR and NRR Diesel?
Circuit
Wire color
Location and what it does
BrakePositive +Not yet checked
Green (trailer connector)
Red, thin wire (behind the radio)
Trailer connector H-172, left inner side of the frame rail, behind the transmission crossmember, pin 1. Or the thin Red wire in the brake controller pigtail behind the radioStop lamp output at the trailer connector. The thin Red wire behind the radio only works after a relay is fitted in position R-9 of the relay console, and Isuzu does not supply that relay.
DoorsNot foundNot yet checked
Not found
Not foundWe found no source for this wire.
Parking brakeNot foundNot yet checked
Not found
Not foundWe found no source for this wire.
HazardNot foundNot yet checked
Not found
Not foundWe found no source for this wire.
Trailer supplyPositive +Not yet checked
Red/White
Trailer connector H-172, left inner side of the frame rail, behind the transmission crossmember, pin 8Supply power for a trailer. The fuse that feeds it was not confirmed.
Vehicle speedNot foundNot yet checked
Not found
Not foundWe found no source for this wire.
CAN busNot foundNot yet checked
Not found
Not foundNo CAN wire or diagnostic port pin was found for a 2015 truck.
Source: Isuzu's 2015 body builder guide for the diesel N-Series (Section 17). Doors, parking brake, hazard, speed, CAN and the diagnostic port location were not found for 2015. On a 2023 NRR, one telematics maker puts the OBD port in the driver side left foot well.
Which years share wiring with the 2015 Isuzu NPR-HD, NQR and NRR Diesel?
This page2015 dieselNPR-HD, NQR and NRR.
Same wiringNone confirmedNo source shows which other years use these wires. This cab style started with the 2008 model year.
Not this pageGas trucks, other years and the Chevrolet Low Cab ForwardNo wire colors were found for them yet. Isuzu publishes a body builder guide for each year, and those guides are the place to check.
Where are the fuse boxes and ground points on a 2015 Isuzu NPR-HD, NQR and NRR Diesel?
InteriorRelay console in the center of the dash, just above floor levelPosition R-9 in this console is the brake signal relay. The fuse box location was not found in text.
Under the cabBrake controller supply harness, behind the passenger side headlightIt plugs in just inboard of the right frame rail, beneath the ABS control module. Until it is connected the battery feed behind the radio is dead.
Ground pointsBlack wires at each plugBehind the radio, J-118 pin D, J-111 pin 2 and H-172 pin 5. No named ground point was found.
From the 2015 Isuzu body builder guide. No fuse list was found for this year, so no fuse tap position is given.
Where is the OBD-II port on a 2015 Isuzu NPR-HD, NQR and NRR Diesel?
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 2015 Isuzu NPR-HD, NQR and NRR Diesel wiring
What wire is constant power on a 2015 Isuzu NPR-HD, NQR and NRR Diesel?
Red/Green at the trailer brake controller wires behind the radio (heavy gauge wire). Battery feed for a brake controller, fused at 20 amps. Meter it before you tap it.
Where is the reverse wire on a 2015 Isuzu NPR-HD, NQR and NRR Diesel?
Red/Blue (positive +) at the back up alarm connector J-111, left inner frame rail, behind the last crossmember, pin 1. Back up alarm supply. Meter it before you tap it.
Where is the brake wire on a 2015 Isuzu NPR-HD, NQR and NRR Diesel?
Green (trailer connector) and Red, thin wire (behind the radio) (positive +) at the trailer connector H-172, left inner side of the frame rail, behind the transmission crossmember, pin 1. Or the thin Red wire in the brake controller pigtail behind the radio. Stop lamp output at the trailer connector. Meter it before you tap it.
Which years share wiring with the 2015 Isuzu NPR-HD, NQR and NRR Diesel?
None confirmed. No source shows which other years use these wires.
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