Holley Instructional Video: Holley EFI Main Harness Overview

Watch as Holley Engineer Doug Flynn walks through the various connectors on the Main Harness.

Transcript: This is the main wiring harness for a Holley Avenger, HP, or Dominator system. This particular harness is for a four barrel TBI. All of the harnesses are similar. Although this may look complicated, its really pretty simple. All of the connectors are labeled to tell you what they plug into. These are the two connectors that plug into the ECU. This loose wire here, which is red with a white stripe, needs to go to a switched ignition power source. This power source must be active when the key is in the run position but also, importantly, in the cranking position. If your vehicle won't start, the first thing to check is to make sure that the source that you connect this wire to has power when the engine is cranking.

This fuse is for the fuel injectors and fuel pump. This relay is for the fuel injectors and the fuel pump. This is a CAN bus wire. If you're using the option Holley full-color touch-screen LCD you plug into this port. Towards the middle of the harness is what's labeled the input/output connector. This is for four inputs and four outputs that are optional. You can do things such as turn an electric fan on. You can purchase an optional connector that plugs right into this with the wires should you desire.

Next in the harness we find five loose wires. Detailed instructions on how to connect these is included in the instruction manuals but I will briefly review. The black wire is just a ground wire that needs to go to a good chassis ground. This does not need to go to the battery but just to a good solid chassis ground. This red wire is a battery power source that feeds the relay for the fuel injectors and fuel pump. This can go to the battery or to a source for a constant 12 volt feed. This green wire is the 12 volt wire that goes to the fuel pump. If you have a fuel pump that takes less than 10 amps you can directly use this wire to power the fuel pump. If your fuel pump draws over 10 amps you need to have this trigger a separate relay. This yellow wire is an RPM input if you're using various distributors. Consult the instructions for proper wiring of this. And finally we have the white wire. This white wire is also used in the ignition wiring for some applications. Consult the instructions for this as well.

Next we have a three pin connector for knock sensors. Holley offers various adapters to plug into this if you're using one-wire or two wire knock sensors. This ten-pin connector marked IGN is for your ignition. Holley offers various adapters to go to different styles of ignition systems. Consult the manual for proper wiring of the ignition adapter.

This ten-pin connector is for the fuel injectors. It's marked INJ. This plugs directly into the injector harness that's supplied with your kit, whether you use TBI injectors or multi-port fuel injection.

The following connectors all plug into the various sensors. They are all labled. This one's labeled FUEL. It plugs into an optional fuel pressure transducer if you want to monitor your fuel pressure. This is labeled MAP for MAP, that's the MAP sensor. This is labeled IAC for idle air control motor which is mounted on the throttle body. That plugs into that. This is labeled TPS for the throttle position sensor. It plugs into the throttle body as well. This is labeled MAT for manifold air temperature. It plugs into the manifold air temperature sensor. This is labeled CTS for coolant temperature sensor. It plugs into the engine coolant temperature sensor. And finally we have labeled WBO2, its for the wideband O2 sensor which is located in the exhaust system. These all all plug-and-play and once you plug them in you're ready to go.