I am currently building a custom MegaSquirt harness for my Mega Squirt III setup on my car. I build an adapter to interface into the stock harness to get everything up and running as close to stock as possible. Once I had that working well I pulled all the stock harness out and I'm just about done building a new harness to directly plug into the MS3 ECU with MS3X for sequential injection and distributorless ignition. It interfaces directly with the stock body harness so you don't need to cut your harness up and can easily return the car to it's stock form.

The stock engine harness is basically garbage. I have yet to see an original one where the shielding on the Dizzy side is still in good condition but given that it's exposed to the elements it's not fair to expect it too be. There is basically no shielding on anything other than the O2, the fuel pump control (don't care with MS) and the dizzy. An auto engine bay is full of EMI that can cause problems with any electronic fuel injection system. Look at a 240SX wiring diagram and you'll see that the manufacture shields almost all of the sensors. I've been researching a few other after market engine harnesses for other engines to see what the other guys have. The 2JZ, etc have a lot of after market stuff and they boast Raychem this and MIL spec that but only bits and pieces are they way they should be. I've seen a lot of "quality" harnesses that boast MIL spec and yet the sensor signals travel over a single vinyl coated wire. So again out of frustration we are left to do it ourselves. Fortunately this is my area of expertise and I'm currently developing a EMI hardened engine harness for the S130 and will be designing one for the S30 chassis. The basic design will allow for a plug and play to the stock body harness (on the S130 at this point in time - haven't done my homework on the S30 yet) to control the stock fuel pump relay and fuel pump circuit (the S30 harness will have it's own fuel pump control). It will have its own fuse system and relays. The main intent is performance first (EMI hardened and the highest quality cabling, etc) and asthetics as an important secondary. You should be able to pull out your stock S130 harness and plug this harness in with an excellent fit and finish. If you ever want to go back to a stock setup simply unplug the aftermarket and plug in the new harness - no cutting into anything. Currently the design has all sensors shielded and cabling for your Wideband 02 with fused power and shielded input. The knock sensor and CHTS are not used with MS3 but are included (shielded of course) in the harness should you wish to use them. There is the capability to unplug the injectors from a built in adapter to go from batch fire to plug directly into the 3X board for sequential injection. An optional crank fire or distributorless ignition harness is also being developed. Since each configuration may have slight variances as to where sensors are located each harness can be built for the particular application.

Working on a custom car can be frustrating under normal circumstances but trying to chase electronic gremlins can be a nightmare even for an Electronics Engineer. The purpose here is to have a harness that starts you off from a solid base so you aren't chasing your tail and you can concentrate on the rest of your build. Let me know what you guys think and what you would like to see from a properly engineered quality custom harness.