Engine Harness & Wiring Parts

So a few weeks back I started working on the ECU/engine harness, this was re-using old connectors and terminals. Was never happy about re-using those parts...

How it was with the re-used parts.

Fortunately I was able to find the part numbers for new parts, all sourced locally from RS Components too! All parts are manufactured by Tyco/AMP and the part numbers are below:

I also found a very good source for automotive wiring in Brisbane, the company is CECA and located in Geebung. They stock Tycab's full range of automotive cabling.

All new connectors and terminals!

Also started on my Deutsch connectors, love these things!

All terminated... this connector is used for all coil and injector +12V wires.

As a precaution, I also did continuity checks for every wire and terminal used.

These are the parts I picked up to do my dedicated fuse/relay panel. Includes terminal bar, bus bar, fuse block and a relay block.

On the left are the brand new terminals I used, and the right is the FD RX-7 battery fuse block. This is where I'll be relocating all my main fusible links, sits on the positive side battery clamp.


Custom Wiring Harness – Part 2

Over the last couple of days I finished off the main body harness, it's basically just wiring for the exterior lights and all in-cabin stuff plus fuses. It started out as a big mess but I think I did a pretty decent job in cleaning it up, also was able to relocate the engine bay fuse box to under the dash.

Another thing I did was remove all the stupid tape Mazda used on "wire splits" and replaced it with heat-shrink, I HATE TAPE!

I used zip ties instead of tape to bundle the wiring harness, all engine bay wiring will have convoluted tubing to protect it from stuff.

Removing the stupid tape and replacing it with heat-shrink.

Main body harness completed, now to start on the power and engine harness...


Custom Wiring Harness – Part 1

I decided that since my car would be off the road for a month or two as I work on the engine, it would be a great chance to do a custom wiring harness for the car. This would mean the body and engine/ECU wiring harnesses would be separated and independent of each other. Try to keep it all as simple as possible, will be especially nice to have a dedicated harness for the Megasquirt =)

So I was lucky enough to pickup an entire wiring harness (body, main, power, dash) for a decent price and got started working on it.

I've stripped the following from the harness so far:

  • All engine wiring
    • Air Flow Meter
    • Ignitors & coils (going COPs for the Megasquirt)
    • IAC valve
    • Purge valve
    • O2 (going dedicated wideband)
  • AC stuff
  • Power-steering
  • Clutch switch
  • Neutral switch
  • Fan switch (Megasquirt will control fans)
  • probable more... can't remember

All engine/ECU related fuses and relays will be kept separate and located close to the ECU. The engine bay fuse/relay box will be made redundant and relocated under the dash as there will only be four fuses used at that location.

After a long day of peeling tape and cutting wires...

99% complete with the main harness, you can see the pile of tape and wires removed in this photo. Seems a bit excessive doesn't it?

This is the wiring kit from DIYAutoTune, pretty handy. Will be used for engine to ECU wiring.

I then spent the rest of the afternoon de-pinning the ECU terminals so I could salvage the pins to re-use. It sucks having a budget...


Wiring Harness

This weekend we tackled the wiring harness.

The MX-5's engine and body wiring is pretty much one single harness, a huge pain in the ass if you just want to remove the ECU and engine harness. While the harness was out we decided to remove all unnecessary wiring, doesn't have to be done but sure makes for a neater harness. Was a big task ahead of us...

Started off by removing any clips and disconnecting the harness, removing the after-market alarm/immobiliser, and then the blower/heater/air-con boxes.

Read more after the break...


Hazard Switches Installation!


OK! I'm excited for my new Hazard Switches kit 🙂

Item can be purchased below, use the shopping cart if you're in Australia, or use the PayPal button below (and in the product description) if you're located outside of Australia. Prices are in Australian Dollars and shipping is built into the price.

Hazard Switches! (International Shipping Included!)


Now the first job before installing your new Hazard Switches is to remove the tombstone. I won't go into this step because there are dozens of tutorials that already exist online. The YouTube video below is pretty good.

This is how you'll receive the kit, comes with the "plug & play" harness, switches, panels and brand new sticker.


Take note of the labelled bags and the markings on the face plate and switches.


Install the switch marked "R" in the top position of the face plate, and switch marked "B" goes in the bottom position. Switch locations and orientation are marked on the back of the face plate.


Once the switches are in, you can go ahead and install the backing plate and carefully tighten the nuts until finger tight, making sure the switches and face plate are in position. Once the nuts are finger tight, grip the switch housing and rotate counter-clockwise to further tighten down the switches.


The connector labelled "R" plugs into the top position, and connector labelled "B" goes into the bottom switch.


And this connector plugs into the factory wiring.



Wiring Complete!

So here we are, all done.. All those early mornings before work and late nights after work building the engine harness and tucking the body wiring. Pretty happy overall with the finish product, just a few changes I will make later. Just want to get the car running for now.

The 3D printed plate will be replaced with a laser cut stainless steel piece.


Engine harness complete!


Dummy fitted the intake so I could cut the injector wiring to length.


The start of the ECU side of the engine harness. All this is being recycled from the previous wiring setup. So handy having everything done with Deutsch connectors.


Terminating the shielded wires for the crank, cam and TPS sensors.




The washer bottle has been relocated to under the guard, I think it should clear everything on full lock and compression. It's a bit awkward to refill, but probably only needs to be topped up once a year. This washer bottle is from a Holden HQ I believe.





OK, a decent update. Lot's of photos.

Because I'm planning to use bulkhead connectors on the firewall for the engine harness, I drew up this plate to mount the connectors. It allows easy disassembly if any changes need to be made or replacing connectors etc. Because I'm recycling parts for this section, the connectors used are Deutsch 12-way DT and Deutsch 31-way HDP.

Had it 3D printed so I could start the wiring while I wait for the real thing to get laser cut from stainless steel.



Headlight assemblies in.


Brake booster, clutch master and radiator in.


Installed these Garage Star Fender Braces too. Pretty straight forward, comes with all new stainless steel bolts.


Because I had the valve cover sandblasted and painted, all the baffles need to be removed so the blast media can be cleaned out. Garage Star machined stainless steel valve cover bolts. I've got a whole engine bay dress up bolt kit to go on too.


Started on the body wiring tuck, wires are coming out of the side behind the front guards. This has been drilled, painted and sealed to keep moisture out.


Slowly cleaning it up and routing. I've used loom tubing for exterior sections, they provide more protection than just braided sleeving alone.


The wires re-enter the body from the side, drilled a 24mm hole and than sealed any bare metal. Ideally I should have done all the cutting/drilling before paint, lesson learned. I also picked up these wiring grommets from Clark Rubber.


I've had to make a few extensions to tuck the body wiring. Instead of soldering, I've been using these uninsulated butt-splice crimps and than heat-shrinking over it.


Using a factory hole to tuck the wiper motor wiring. I think the hole is normally used for the washer hose, but I'm relocating the washer bottle... More details on that later.


These exposed wires have been wrapped and loom tubed now. Interior sections are covered in a braided sleeving with heat-shrink on the ends.


The headlight assemblies back in, most of the wires are out of sight.


The dual horns installed, and the body harness is done!


Just so everyone knows, this part of the build is on a strict on budget, won't be MIL Spec or anything like that. Every part was either given to me for free or simply re-used from my old harness. It'll do for now, and I'll look into doing a concentric twisted MIL Spec harness later.

Below is the wiring for the coils, it is being terminated into a Deutsch 12-way DT connector. This connector contains wiring for the coil triggers (x4), coil power (x4) and the ECU grounds (x4).


For shielded wires (TPS, crank and cam sensors), what I did was strip the cable further back and unbraided the shield. I than twisted it up and heat-shrinked. It gets terminated into the bulk-head connector and continues onto the other side.


Finished the crank and cam sensors. This is all a dry fit, once I have it mostly sorted, the wires will be sleeved and heat-shrinked.


To tuck the starter and charge wires, I had to a slight extraction and feed them through the tunnel.


So my ITB manifold is shit... The factory Toyota manifold has two dowels per throttle body to locate everything into perfect alignment. If the throttle bodies aren't correctly aligned than they don't open equally no matter how many linkage adjustments are made, not great at all!

Below is my solution. I mounted my throttle bodies to the Toyota manifold, adjust everything and confirm their alignment. I than bolt the tops of the throttle bodies to a thick plate of steel. The throttle bodies are removed from the Toyota manifold and transferred to my Techno Toy Tuning manifold. DONE! Everything is spot on now.


Many late nights...



Back Home!


Happy day! Car has been towed back home and first thing we did was remove all the front panels 🙂 Storing them in a spare bedroom for now, don't want to scratch anything during assembly.


Colour is Audi's Aviator Grey.


The entire engine bay was covered in blankets during the engine install.




Colour looks amazing in sunlight, the Audi paint code has a bit of pearl through it but can only be seen in direct sunlight.


The freshly powder coated radiator and sway-bar brackets fitted up with new bolts.


A quick mock up panel for the engine harness Deutsch bulkhead connectors.


I had the front lip painted gloss black, will be interesting to see how well it holds up from all the abuse it cops 😛



Respray Preparations.


As some of you may know, the MX-5 is booked in for a re-spray and engine bay colour change. Body will be painted factory Crystal White and the engine bay will be Battleship Grey. Now the stripping and preparations begin!

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Seats were removed to make it easier to pull the dash out. Dash came out so I could pull the wiring harness completely back in to the cabin.


Rest of the parts being stored away. The ARP CF mirrors getting sanded back and a new coat of clear too.


Pop-up headlight assemblies will be disassembled and sand blasted, they'll be painted same colour as the engine bay.


Part way through the long and slow process of removing everything from the engine bay.


Head Unit Relocation 2nd Update.


Received some feedback and discussion on my head-unit relocation last week, and as I often find, I decided to change it up to the better option.

Below are photos of where the head-unit was mounted, I made a custom MDF piece for that spot too.


But it was obvious that the better position would be in the other corner of the boot, and mounted from above. Overall it looks a lot cleaner and more out of the way.

Started off by half removing some of the rear carpet, I than removed the bottom four bolts of the rear parcel shelf cover. Made it a lot easier to run the harness.


Harness fed through and the head-unit case mounted up!


Everything mounted and connected, works just as well as before.