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Holley Terminator X wiring diagram: J1A / J1B pinout

Connector J1 on a Terminator X or Terminator X Max is two plugs: J1A (34-pin, next to the USB connector) and J1B (26-pin). J3 is drive-by-wire. J4 is the transmission. The HP and Dominator use the same pin numbers. Below is where those pins land on an LS, which kit is 24x or 58x, and how the power wires are fused.

Last updated November 8, 2026

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Terminator X wiring diagram

People looking for connector J1 want two plugs. J1A is the first connector next to the USB connector, 34 pins, mostly inputs. J1B is the second connector, 26 pins, mostly outputs (eight injectors plus the coil drivers). J2A and J2B are not a second name for those plugs. On a Dominator they are extra connectors the HP does not have: J2A is a second wideband plus more inputs, and J2B is four more injector drivers, four more coil drivers, and more outputs. The Terminator X connector names are J1A, J1B, J3, and J4. There is no J2 in that list. J3 is the drive-by-wire harness. J4 is the transmission harness. The HP, Dominator, Terminator X, and Terminator X Max share these J1A and J1B pin numbers. Full tables: J1A and J1B. Wire colors are not printed on those ECU pins. Colors below are only the loose wires and the input/output plug.

The Terminator X ECU is 554-152 (CARiD). The Terminator X Max ECU is 554-153. A base Terminator X kit is cable throttle only: the wizard questions for throttle-body type and transmission control are Terminator X Max only. An X Max kit includes drive-by-wire, a transmission harness, or both. The part number shows which. Diagnostic LEDs on the ECU show power, engine run, wideband status, TPS calibration, crank, and cam, which splits a no-start into power, sync, or the throttle cal. Mount it in the passenger compartment when you can, with those LEDs facing up. In the engine bay, keep it out of direct water and road debris, away from headers, and as far from plug wires and a capacitive-discharge ignition box as you can. Point the connector end down so water cannot run into the terminals. Do not over-tighten the mounts if the surface is not flat. If the ECU is in the cabin and the firewall has no hole, cut a 2 in hole and fit grommet Earl's 29G001ERL. The handheld plugs into either CAN connector, about 21 in from the ECU, and it can come out of the car once setup is finished.

Where each LS circuit lands

These are the same pins as the tables further down, named for the LS part they serve.

Wideband placement: put the bung where the cylinders on that bank have already merged, not far downstream. On long-tube headers that is about 1 to 10 in after the collector, with at least 18 to 24 in of pipe after the sensor. If the car has catalytic converters, the sensor has to sit between the engine and the converters. Mount it in the upper half of the pipe, tipped more than 10 degrees, so condensation does not run into the sensor. The hole is 7/8 in. Anti-seize goes on the threads only. Keep it off the sensor tip. Running the engine with the sensor installed but unplugged damages the sensor. Until it is plugged in and powered, close the hole with an 18 mm oxygen-sensor plug or an 18 mm spark plug.

24x vs 58x kits

Two things on the engine side change with the crank pattern, and both have to match the engine in the car, not the engine name. The main harness is 558-102 for a 24x crank and 1x cam (labeled LS1, 24x) or 558-103 for a 58x crank and 4x cam (labeled LS2/LS3/LS7, 58x). Most LS2 engines are 58x/4x. A few early LS2 engines are 24x/1x and use 558-102, the same harness as an LS1 or LS6. The cam sensor on a 24x engine is usually at the top rear of the block, behind the intake. An early 24x LS2 may have that sensor in the front. Harness 558-102 is built for the rear sensor, so extend its cam-sensor wire to reach a front sensor. Extend only that cam lead. The drive-by-wire harness still cannot be cut or lengthened. A 58x cam sensor is in the driver-side timing cover. In the wizard, pick the crank sensor type that matches the harness you bought. The cam input needs that same match in the software, because the ECU has to be set for the sensor that is actually on the engine.

The injector plug is a third choice, separate from 24x vs 58x. EV1 is harness 558-200, EV6 (USCAR) is 558-201, and truck Multec 2 is 558-214. LS engines left the factory with all three, so the harness has to be the shell that fits the injector. The injector leads are labeled by cylinder. Put each one on that cylinder or severe engine damage can result. Do not re-pin A through H to change the firing order. Every LS uses 1-8-7-2-6-5-4-3, and that order is set in the software.

24x / 1x kits are for LS1 and LS6, for Gen III 4.8, 5.3, and 6.0 truck engines, and for a few early 24x LS2 engines. 58x / 4x kits are for most LS2 engines, for LS3, and for Gen IV truck engines. The 58x harness label also covers LS7. Choose by the crank and cam pattern, not by the LS2 name. Current cable-throttle Terminator X kits (ECU 554-152, no transmission harness):

Current Terminator X Max kits (ECU 554-153). Transmission "4L60E / 4L80E" is harness 558-405, listed as 4L60E (pre-2009) / 4L80E. That harness also fits a 4L65E, an early 4L70E, and a 4L85E. The 4L60E connector is vertical on the passenger side. The 4L80E connector is horizontal on the driver side. Output speed is the rear passenger sensor on a 4L60E and the rear driver sensor on a 4L80E. A 4L60E has no turbine-speed sensor. A 4L80E has one on the front driver side. The ECU only monitors that 4L80E sensor. It does not use it in any calculation. A 4L70E has one inside the transmission. This harness does not connect it, so the ECU does not see it.

6L80/6L90 control needs a Terminator X Max. Harness 558-499 is 2WD only, does not support 4WD, and needs software version 3.0 build 100 (handheld firmware TermX.3.0.100.fwu, ECU firmware SNEFI_03001000.eep). It is for 2007 and later 6L80 and 6L90 transmissions. A 6L80 or 6L90 from before 2007 is outside this harness, and so is a 4WD truck. A 4x4 with an electronic transfer case is not recommended. The harness talks CAN to the transmission's own TCM, which is why that software build has to be loaded before the ECU can use the link. You can move a Terminator X calibration onto a Max ECU after you save it. J3 on this harness is the connector between the MAP tube and the main power plug, and J4 still plugs in opposite the main engine harness. If the same ECU also runs drive-by-wire, J3 is already taken: move the two TCM CAN wires into the drive-by-wire connector. Current harnesses use orange on J3 pin B14 and orange/black on J3 pin B20. Older harnesses used tan and tan/black in those same cavities. Check the cavity and the wire color on your harness before you move a terminal.

Other known options. The same LS harnesses are sold on their own: 558-102, 558-103, 558-200, 558-201, 558-214, 558-406, 558-429, 558-405, 558-499 (2007 and later 6L80/6L90, 2WD only, does not support 4WD, V3 build 100 or later), input/output 558-462, main power 558-308, coil sub-harness 558-321, wideband extension 534-199, and unterminated ignition adapter 558-306. Service ECUs are 554-152 and 554-153. Universal MPFI kits on harness 558-104, instead of the LS plug-in harness, are 550-936, 550-937 (CARiD), 550-942, 550-943, 550-944, 550-945, 550-950, and 550-959. Kits 550-937, 550-943, 550-944, and 550-945 pair that harness with Ford EV1 injector harness 558-209. Coyote kits use main harness 558-110. Modular kits use 558-108, or 558-113 when the coils are the smart-coil type. Hemi kits use 558-115 (early) or 558-116 (late). Gen V LT kits use an LT1 main harness with coil sub-harness 558-321. TBI kits 550-1001 through 550-1003 and 550-1011 through 550-1013 use harness 558-414. Stealth 2x4 kits 550-1004 through 550-1006 and 550-1014 through 550-1016 use harness 558-121. A T on the end of an LS plug-in kit number means USB-CAN dongle 558-443 instead of handheld 553-201. That option is the LS kits in the tables above, except the three 6L80 kit numbers.

Drive-by-wire vs cable

A base Terminator X has no drive-by-wire harness. Drive-by-wire plugs into J3 on a Terminator X Max, and that harness cannot be cut, shortened, lengthened, or have the shield removed. Keep it at least 5 in away from plug wires, coils, ignition boxes, and radios. Where the harness passes through the firewall or other sheet metal, use a rubber grommet so the jacket cannot chafe. The brake-switch wire must see +12 V when the brake lights come on. With the brake applied, the ECU limits throttle position to at most 10% no matter how far the pedal is pushed, and limits fuel flow to at most 30 lb/hr. Release the brake, then bring the pedal below 10%, before a higher throttle position is allowed. The pedal and the throttle body each have two position sensors. If any one of them moves off its calibration, the throttle body is de-powered into limp-home. On the GM throttle bodies this harness supports, that opening flows enough air to move the car at about 45 mph, which is more than idle, so the car needs more brake to hold it in gear. A throttle body from another manufacturer can flow a different amount.

Mount the pedal so it cannot move on its bracket, with nothing in the way of full travel back to idle. It has to sit far enough from the brake pedal that the brake can be fully applied without a foot hitting the drive-by-wire pedal, and the drive-by-wire pedal should sit lower than the brake pedal when the brake is pressed.

Harness 558-406 is the 6-pin plug for passenger cars and later trucks. Harness 558-429 is the 8-pin early-truck plug. The truck years overlap: 6-pin body 12580760 is listed for 2005-2008 trucks, and 8-pin body 12570800 is listed for 2002-2007 trucks, so a 2005-2007 truck can be either shell. On a loose throttle body, the part number picks the harness. Of the LS plug-in kits in the tables above, only 550-927 and 550-930 include 558-429. The other drive-by-wire kits in those tables include 558-406, except 550-928-6. That kit includes drive-by-wire, and the harness part number is not printed for it. The pedal for these harnesses is GM 10379038. Harness 558-406 also accepts pedal 145-160 / GM 19417903. Cable-throttle TPS plug 543-111 and IAC plug 543-34 stay unused on a drive-by-wire install.

More: pedal and throttle-body pinout (every cavity on 558-406 and 558-429, and which GM throttle body each harness fits).

Power, ground, fuse, and relay

An LS kit harness (558-102 or 558-103) has five loose wires, plus the main power plug and the 8-pin input/output plug (mating harness 558-462, about 52 in from the ECU). This is not the universal harness further down the page.

Two more black wires with eyelets are coil grounds, one per bank. The label reads CONNECT TO CYLINDER HEAD ONLY. Bolt them to the rear of each head so the coils have a ground. Some harnesses do not include these wires. If they are on the harness and you leave them off, the coils are not grounded and the engine runs poorly. Coil sub-harness 558-321 replaces the factory coil harness when you want a cleaner run.

Transmission loose wires, when the kit includes that harness:

Common mistakes

• ECU ground on the body instead of the battery. Terminal A (black) goes to the battery negative post. The engine still needs its own ground to that battery and to the chassis. A body bolt with no continuity leaves the ECU and the sensors on a floating ground. On a dual-post battery, give the ECU its own studs on the unused posts so it does not share the posts the other cables already use.
• Chassis ground with no continuity to the engine and the battery, or stacked on the same stud as other grounds. Check the black loose wire with a DVOM. It is a separate point on purpose.
• Coil grounds on the body or left off. They belong on the rear of each cylinder head, one per bank, or the coils have no ground.
• Switched 12 V that dies in Crank, or taken from a coil, an audio circuit, or HID headlights. The red/white wire is about 7 in from the ECU. If that feed drops while the starter is engaged, the ECU loses power mid-crank. A coil, audio, or HID circuit is a dirty source and is not this wire's power.
• 24x harness on a 58x engine, or the other way around. 558-102 is 24x/1x. 558-103 is 58x/4x. Most LS2 engines are 58x, but a few early LS2 engines are 24x and may have the cam sensor in the front. Match the harness to the crank and cam on the engine, not to the LS2 name. The wizard crank type has to match the harness. A mismatch means the software is set for a sensor the engine does not have.
• Injectors on the wrong cylinders, or A-H re-pinned for firing order. A is cylinder 1 through H is cylinder 8. LS firing order 1-8-7-2-6-5-4-3 is a software setting. The wrong cylinder can cause severe engine damage.
• Odd and even coil connectors swapped. Driver side is DIS CONNECTOR ODD. Passenger side is DIS CONNECTOR EVEN. Swapped, the firing order does not happen and damage can result.
• Low-impedance injectors. These ECUs only drive high-impedance injectors. Low-impedance injectors damage the ECU.
• EV1, EV6, and Multec 2 mixed up. 558-200, 558-201, and 558-214 are different shells. The plug has to match the injector on that engine.
• MAP or TPS left unplugged, or no TPS autoset. Key on, engine off, MAP should read 95-102 (as low as 75 at elevation), cable TPS 0 closed and 100 at wide open, battery at least 12.0 V. If MAP, TPS, coolant temp, or battery is wrong, do not start. A new system will not fire the injectors or the ignition until the TPS autoset is done. An empty fuel-pressure connector and an empty oil-pressure connector both read LOW Err in the data monitor, and the handheld fuel-pressure reading is also inaccurate. Neither is a running problem, and neither is a reason to hold the start. If a pump is wired, the key cycle should run it for 5 seconds. Check for fuel leaks before you crank.
• Boost on the internal 1-bar MAP. A boosted combo needs GM 2.5 bar sensor 12592525 and adapter 558-416 (not in the kit). The base calibration expects that sensor. Skipping it can cause severe engine damage.
• Cable TPS and IAC plugs forced onto a drive-by-wire throttle. Those connectors are not used with drive-by-wire. The pedal and throttle body use the J3 harness.
• Fan wired to the fan output, or a relay waiting for +12 V. B12 and B11 (I/O pins E and F, gray/yellow and gray/red) only provide a ground to the relay trigger. A relay coil that expects +12 V from the ECU never pulls in.
• Green pump wire on a pump over 15 A. The LS kit does not include a fuel pump. Check the current rating for the pump you install. At 15 A or under, the green wire can feed the pump. Over 15 A, use that wire to trigger a relay and run 10 gauge to the pump. Pin A2 on the ECU is a separate 10 A max. Give the pump its own chassis ground.
• Transmission red/white tied to the ECU red/white. The transmission harness back-feeds the ECU and the engine will not shut off. Give the transmission red wire a constant source that can supply 5 A.
• Drive-by-wire harness cut or modified, or the brake input left off. The shield is part of the circuit. The brake input is required. While the brake is on, the ECU limits throttle position to at most 10% no matter how far the pedal is pushed, and limits fuel flow to at most 30 lb/hr. Release the brake, then bring the pedal below 10%, before a higher throttle position is allowed. Keep the harness 5 in from plug wires and coils.
• 6L80 yellow wire on a +12 V crank circuit. Yellow is a TCM ground output, grounded in Park and Neutral. Connect it to relay terminal 85, and connect relay terminal 86 to ignition crank/start. A +12 V neutral-safety switch or crank wire on yellow damages the TCM.
• 6L80 CAN wires left in a second J3 when the car is also drive-by-wire. Move them into the drive-by-wire connector. Current harnesses are orange on J3 B14 and orange/black on J3 B20. Older harnesses are tan and tan/black in those same cavities. Check the cavity and the color before you move a terminal. J3 is one plug.
• Wrong wideband, the sensor downstream of air injection, or the sensor installed but unplugged. Use Bosch LSU 4.9 sensor 554-155. An LSU 4.2 will not work. An NTK sensor 554-100 or Bosch sensor 554-101 fits an HP or Dominator, not these ECUs. Leaded fuel degrades the sensor. Some RTV kills it, and so does anti-seize on the tip. Put the bung where that bank has merged, ahead of any catalytic converter, not far down the pipe. Measurements and the tip angle are in wideband placement. A sensor downstream of air injection drives the mixture extremely rich and can damage the engine. Do not run the engine with the sensor in the pipe and unplugged, or the sensor is damaged.
• LS2 GTO or F-body oil-pressure sensor on this harness. Those sensors use a different pin-out. If the factory sensor does not plug in, use 554-102.
• Crank-sensor cable left in the starter heat, or loomed with the plug wires. The sensor is behind the starter. Bundle that cable in reflective heat shielding and route it away from heat. Do not run crank, cam, or other sensor wires in parallel with plug wires or an ignition box. Cross at an angle if they have to cross, and do not let plug wires lie on the EFI wires. On a start attempt the RPM reading should change to Syncing, then show RPM. No RPM signal is a wiring or setup error.
• ECU connector end pointed up in the engine bay. Water runs into the terminals. Point the connector end down, keep the ECU clear of headers and plug wires, or mount it in the passenger compartment.
• T-taps, or a twisted joint with no heat shrink. A t-tap cuts strands and loosens with heat and vibration, so a circuit that tested fine becomes intermittent. Crimp the joint, or crimp and solder it, and cover it with heat shrink.
• A signal wire shared with a second ECU. Do not splice the TPS, or any other sensor signal, so two controllers share it. The extra load changes the voltage both of them read.
• Cam-wire shield grounded at both ends, or extended with unshielded wire. The shield grounds at the ECU end only. An early 24x LS2 with the cam sensor in the front is the lead you may have to extend, and that extension still has to be shielded cable.
• Welding on the car with the ECU still plugged in. Welding current will use the harness as a return. Unplug every ECU connector and take the ECU out of the car before you weld.

Pins by system

J1A connector

J1B connector

B11 and B12 differ by ECU: high-side (H, P+) outputs on the HP and Dominator, ground-side (G, P−) on the Terminator X and X Max.

Harness connectors

Injector connector (A = cylinder 1 … H = cylinder 8)

Holley routes A–H to cylinders 1–8. Don't re-pin for firing order; the firing order is set in the software.

Ignition adapter connector

Knock sensor connector (3-pin Metri-Pack, universal harness)

Wideband O2 connector (8-pin)

Fuel pressure connector (Holley 554-102 transducer)

Oil pressure connector (Holley 554-102 transducer)

CAN bus connector

* Holley's manual has three labeling slips we kept visible: the oil pressure section prints pin C as "Fuel Pressure Signal" (the ECU pin, A20, is the oil pressure input); the wideband section prints "CCOMPR2" (J1A table: COMPR2); and A17 reads "VS-/IP-" in the wideband section but "VS-/IP+" in the J1A table. Pin numbers agree everywhere.

Loose wires on the main harness

This table is the universal main harness (558-503, 558-504, and 558-508). An LS Terminator X kit uses 558-102 or 558-103. That kit's loose wires are the five in Power and grounds: red/white, red, green, black, and blue/white. The yellow coil-minus wire and the white points wire are on this universal harness.

Warning from Holley: never connect the yellow "Coil −" wire to the coil of a capacitive-discharge (MSD-type) ignition; it damages the ECU.

Running drive-by-wire? See the pedal & throttle body pinout. Choosing a computer: Tuning an LS or LT.

Parts on this page: Terminator X · Dominator ECU · HP ECU · 554-102 pressure transducers · Bosch wideband sensors · 558-306 ignition harness

Holley EFI questions

• Stock PCM vs Holley Terminator X for an LS swap
• How should electric fans be wired with a Terminator X / LS swap ECU?
• How do you wire the A/C system when running Holley Terminator X EFI on an LS swap?

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