Custom MegaSquirt DIY EFI Conversion on a Ford 302 Windsor V8
Written By: BottleFed70

Megasquit DIY EFI Introduction
Part 1 – Parts and Equipment Used
Part 2 – Fuel System
Part 3 – EFI Sensors and Hardware
Part 4 – Assembling the MegaSquirt and Wiring
Part 5 – Tuning
Part 6 – Ignition Control and Tuning
Part 4 – Assembling the MegaSquirt and Wiring

Assembling the MegaSquirt II ECU: Wire Loom
Instead of buying a pre-assembled ECU I chose to buy the kit and assemble it myself. While assembling the ECU is not too difficult, it is a time consuming project. It’s probably worth it to spend the extra money and buy a pre-assembled and tested kit. However, I wanted to have the experience of building the ECU myself. Saving about $150 was just an added bonus. The kit I purchased was of excellent quality. It included everything I needed and all of the components were nicely packaged with excellent labeling. Pictured below is the kit as it arrived in the mail.

There was probably about 50 or 60 little baggies like this with different components in them.

Assembling the MegaSquirt ECU was a lot easier than I expected. The step by step instructions are very clear and thorough. It’s not something I would recommend to someone who’s never used a soldering iron. But you definitely don’t need to have a lot of knowledge either. The instructions show you exactly where to mount each component, and make sure to warn you when the component needs to be mounted in a certain fashion (polarity for example). Pictured here is the ECU in the early stages of being assembled.
Wire Loom
The full assembling and initial testing process took me about 12 hours to complete. I actually found myself enjoying the time spend soldering the ECU together. It’s very much like building a model car. Below is a picture taken a little further along in the assembly process. At certain points throughout the assembly, the instructions walk you through a way of testing the circuits that you’ve just finished assembling. This allows for a much simpler troubleshooting process if the ECU isn’t working properly. Here you can see that I have the stimulator connected to the ECU and I’m using my laptop to see if the input circuits are functioning properly.

Wire Loom Wire Loom Here’s a picture of the ECU fully assembled except for the top cover. The whole assembly process went very smooth and I was very happy with the results.

Relay Board:
Wire Loom Wire Loom
The relay board was almost a no-brainer. There was only a handful of components and pretty much only 1 way to install them all. The relay board took only about 1hr to assemble and turned out great. What I decided to do was build a wiring harness based around the relay board. I laid out all of the wires I would need and cut them with plenty of length. Later when it was time to install the harness I would trim the wiring down to length and add the needed connectors.

This harness along with the relay board will connect off of the electrical components of the EFI system. This includes: The sensors, fuel pump, ECU, fuel injectors, O2 sensor and controller, and ignition control (for later use).

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I decided to mount the relay board to passenger side shock tower on the side facing the firewall. This area leaves me access room should I need to replace a fuse or relay, yet manages to stay out of view not too badly.

Wire Loom
Here you can see the finished portion of the wiring harness for the engine. There is a connector for the coolant temperature sensor, the intake air temperature sensor, the idle air control motor, Throttle position sensor, and the fuel injectors.

Installed Setup:
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This is what the wiring looks like with everything connected except the intake air temperature sensor.
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Here’s a picture of the engine compartment with everything installed. As you can see, it’s difficult to tell this is not a carbureted engine and I didn’t really put much effort into hiding everything. If you were to move the relay board and coolant temperature sensor to a more discrete place, you’d really have a hard time telling.
  Wire Loom

Another shot of the engine bay.

Part 5 – Tuning