When working with Holley EFI, you’ll
quickly notice that they use a variety of connectors across their main
harnesses. Depending on your specific build, you may find yourself
needing to modify or re-terminate sections of the harness to match your
setup.
The purpose of this
post is to help identify common connectors and associated parts used in
Holley EFI harnesses—specifically for those doing Ford small-block
swaps.
⚠️ Note: This is not a complete list of every connector for every Holley harness. Instead, the focus is on the two most common harnesses used in Ford applications:
-
558-128 Main Harness – Found in Holley kits 550-937F and 550-943F
-
558-104 Main Harness – Found in Holley kits 550-937 and 550-943
While these harnesses appear in other kits, the ones listed above are the most commonly used in the Ford EFI swap community, especially for Small Block Ford (SBF) platforms.
ℹ️ Don’t see the connector you’re looking for?
If there's a connector not listed here that you need information on, feel free to send us a message! We're happy to help and will work on getting it added to the guide to support more builds.
Main ECU Connectors: What You Need to Know
Let’s begin by identifying the main ECU connectors found on Holley EFI systems.
- Holley HP and Terminator X feature two primary connectors:
- J1A
- J1B
- Terminator X Max includes these additional connectors:
- J3
- J4
- Dominator includes these additional connectors:
- J2A
- J2B
- J3
- J4
Regardless of which ECU you have, all systems share the same power connector design, which is important when planning your layout or building custom harnesses.
Main ECU Connections:
| Connector Name | Manufacturer / Type | Part Number | Terminal Part Number | Terminal Seals | Cavity Plug |
J1A | TE Connectivity (AMP) / SuperSeal | 4-1437290-0 | 16-18 AWG: 3-1447221-4 | Not Applicable | 4-1437284-3 |
| J1B | TE Connectivity (AMP) / SuperSeal | 3-1437290-7 | 16-18 AWG: 3-1447221-4 | Not Applicable | 4-1437284-3 |
| J2A | TE Connectivity (AMP) / SuperSeal | 4-1437290-1 | 16-18 AWG: 3-1447221-4 | Not Applicable | 4-1437284-3 |
| J2B | TE Connectivity (AMP) / SuperSeal | 1473416-1 | 16-18 AWG: 3-1447221-4 | Not Applicable | 4-1437284-3 |
| J3 | TE Connectivity (AMP) / SuperSeal | 3-1437290-8 | 16-18 AWG: 3-1447221-4 | Not Applicable | 4-1437284-3 |
| J4 | TE Connectivity (AMP) / SuperSeal | 1473416-2 | 16-18 AWG: 3-1447221-4 | Not Applicable | 4-1437284-3 |
| Power | Aptiv / Duncon 6.3 Series | Connector: 12147067 | 10 AWG: 12147474 | 15324996 | Not Applicable |
Remaining Connections:
| Connector Name | Manufacturer / Type | Part Number | Terminal Part Number | Terminal Seals | Cavity Plug |
| Coolant Temp (CST) | Aptiv / GT-150 Sealed | Connector: 15449028 TPA: 15305024 | 18 AWG: 15326267 | 15305351 15366022 | Not Applicable |
| Manifold Air Temp (MAT) | Aptiv / GT-150 Sealed | Connector: 15335987 CPA: 15317832 TPA: 15305024 | 18 AWG: 15326267 20-22 AWG: 15326266 | 15305351 15366022 | Not Applicable |
| Wide Band Oxygen Sensor (HP/Dominator) | Aptiv / Metri-Pack | Connector: 12047931 TPA: 12047935 | 18 AWG: 12045773 20-22 AWG: 12077628 | 15324976 | 12059168 |
| Wide Band Oxygen Sensor (Terminator X) | Bosch | 1928404669 | 1241380-1 (TE/AMP) | 171805-A (TE/AMP) | Not Applicable |
| Fuel/Oil Pressure | Aptiv / GT-150 Sealed | Connector: 15477863 TPA: 1545268 | 15326266 | 15305351 | Not Applicable |
| Ignition / Crank and Cam Sensor (Main Connector) | Aptiv / Metri-Pack | Connector: 12065425 TPA: 12177082 | 12048074 | 15324973 | 12059168 |
| Manifold Absolute Pressure (MAP) | Aptiv / Weather-Pack | 12020403 | 18-20 AWG: 12089040 22-24 AWG: 12089307 | 15324985 15324983 | Not Applicable |
| Throttle Position Sensor (TPS) | Aptiv / GT-150 Sealed | Connector: 15477863 TPA: 1545268 | 15326266 | 15305351 | Not Applicable |
| Idle Air Control (IAC) | Aptiv / GT-150 Sealed | Connector: 15354716 TPA: 15305028 | 18 AWG: 15326267 20-22 AWG: 15326266 | 15305351 15366022 | Not Applicable |
| Fuel Injectors (Main Connector) | Aptiv / Metri-Pack | Connector: 15324504 TPA: 12045810 | 18 AWG: 12045773 20-22 AWG: 12077628 | 15324976 | 12059168 |
| CAN / CANbus | Molex / Mizu-P25 | 52116-0411 | 50038 | Not Applicable | Not Applicable |
| Power Tap | Aptiv / Metri-Pack | 12162144 | 18 AWG: 12048074 20-22 AWG: 12084200 | 15324976 | 12059168 |
| Input / Output | Aptiv / Metri-Pack | 12047937 | 18 AWG: 12048074 20-22 AWG: 12084200 | 15324976 | 12059168 |
Parts last updated: August 22, 2025
Where to Buy:
Here is a list of preferred vendors that you can go to and purchase some if not all of the parts you need, some even offer kits which come with the connector, locks, terminals and seals.
Corsa Technic - https://www.corsa-technic.com/
Monkey Fab - https://monkeyfabgarage.com
Scarlett Solutions - https://scarlettssolutions.com/
DigiKey - https://www.digikey.com/
Mouser - https://www.mouser.com/
