Now that I have the wiring harness adapted from the standard MX-5 loom, it’s time to install the MK Indy Wiring Loom in the car. This is where the previous hard work starts to pay off, and you start feeling you have achieved something!
Testing the Harness
Before I got too far, I wanted to check that everything still worked after removing so much wiring. So I roughly laid the main harness in the car and connected up the engine harness, ECU and clocks. I connected up a fully charged battery and tried to start the car.
The engine cranked, but it didn’t start… Not what I needed, my heart sank… My mind started racing, had I removed something I shouldn’t? Maybe it was the immobiliser stopping it. Then my son piped up, “Have we plugged everything in?” my immediate reaction was Yes, of course we did! Then I remembered I hadn’t plugged in the rear loom, not thinking it was needed. But this is pretty critical if you want the fuel pump to work!
So we quickly plugged in the rear loom and tried again. This time, the engine fired into life almost immediately! What a relief it was working OK. I couldn’t run the engine for long as we still didn’t have any coolant in the system, but it was running for just enough time for me to check the voltage on the battery, and it was showing a healthy 14.5v. So this meant that the re-wiring of the alternator was working well!
Materials Used
For covering and finishing the wiring harness, there were several different options for me. The approach by MK is generally to use plastic split conduit. This is OK for some areas, but not the prettiest and also not that flexible. I looked at my options and decided on the following main approaches:
Loom Tape
Loom Tape was used to hold the loom together and get it into shape. Also I used it for finishing off the ends of the loom near the connectors. Amazon Link.
Braided Split Wire Loom Wrap
This is a braided material-based split conduit used for most of the loom. I used 3x different diameters (8mm, 12mm and 20mm). Held in place with loom tape. Amazon Link.
Braided Cable Sleeve
This was used to cover some of the slimmer elements of the loom before putting on the end connectors (e.g. Lighting connectors). I used 2x different diameters (6mm [1/4″] and 4mm [5/32″]). Amazon Link.
Heat Shrink
This was used to cover bare wires when extending the loom to fit the chassis. It was also used to help finish the ends where the Braided Cable Sleeve was used. Ebay Link.
Connectors
I used the supplied Econoseal connectors from MK, plus I bought a few more from eBay to provide some future proofing.
- I kept the wiring for the windscreen wipers and washer. So I added a 6-way connector there to the loom so I can just plug into that later when I add a screen.
- I added a 2-way connector near the front left headlight, which is connected to the wiring for the old carbon fuel canister. This provides a feed for a boost controller later on if I go turbo. This will save me running wires later.
- I added a 2-way connector to the 3rd stoplight in the boot area. This is so I can add a high-level stoplight more easily. As you build the loom, think about what you might want later, as it’s easier to add now.
- I added the wiring for a second USB charger socket, through to the rear boot area. This is so I can plug a GoPro into it when mounted om the roll bar.
Earth Points
The manual isn’t very clear as to what to use as the earth points. This is a pretty critical feature of you want anything to work. The general practice of less is more applies here. If you have too many earth points it will be more difficult to track down an earth issue later on. I have gone for 5 earth points in total, which is a lot less than the original Mazda loom.
Engine Earth
As covered in my engine install post I have the engine earthed from the block to the Engine mount with a brass earth point my Dad made for me.
Battery Earth
I wanted a good solid battery earth direct to the chassis but didn’t fancy having it going through a rivnut. So, I decided the right-hand side of the passenger footwell was a good option as it is a solid steel plate welded to the chassis and easy to access and not far from the battery location. I drilled an 8mm hole and used a Dremel to grind off the paint, the same size as a large ‘penny’ washer. Then I used vaseline on the bare metal, which is an excellent conductor, but also will stop rusting and bolted the end of the battery negative terminal to it. I had added a large M8 crimped eyelet to the end with heatshrink. This is a nice, neat solution.
Front Loom Earth
At the front of the chassis, a welded earth point is located just under the throttle body location on the engine. I’m not sure why this wasn’t welded on the opposite side of the chassis, where there is naturally more room, but it is just about reachable once the engine is in. I grouped together a bunch of earth’s in the loom into a soldered multijoint. I then used a large eyelet to connect this to the chassis.
Rear Loom Earth
When adapting the rear loom, I consolidated the earth’s down to a single earth point. This point was quite central to the loom and fitted nicely onto the same M6 bolt as the brake Union in the middle of the chassis at the rear. It used the OEM original eyelet as well so a neat solution.
Dash Earth
There was one earth point near the dash board that is linked into all the other earth’s. I did consider deleting it altogether and just relying on the front Loom earth. I ended up leaving it as a seperate earth nearer the dash. So, I simply drilled a hole in the steering column bracket on the chassis. Then I scraped away and sanded back the paint to leave bare metal. I then used some more vaseline and a washer to mount the earth eyelet securely. This seemed a nice neat solution.
Engine Harness
Next, I addressed the engine harness as it was already a complete harness and did not need further extending; therefore, it just needed wrapping. This was a good test case to try out all the material I had bought for loom wrapping and finishing. I started by using the loom tape to spiral wrap the main parts of the loom and then wrap the ends of some of the thinner wires. This gave the loom a good shape. I checked that it would still fit and adjusted the lengths to be just right.
Then I added the Braided Split Wire Wrap over the top and held it in place with more Loom Tape. This worked very well with the braided wire wrap being very easy to cut and seal with a flame to work around junctions in the loom. The combination of the braided wrap and the lom tape gave an OEM+ type feel. Better than the original Mazda attempt at wrapping the loom!
Front Loom
Next, I decided to tackle the job I was least looking forward to, the extension of the loom and the wiring of the headlights. I had already watched the MK Sportscars very good 5-part series on wiring on YouTube. I commend you to watch this before you do anything, as it provides a great overview of how to tackle the front and rear looms and what to look out for.
From my previous work of stripping back the MX-5 loom, I had already grouped together the wires that needed to go down the right side of the engine past the inlet manifold. These are:
- Headlights (high beam/ low beam)
- Side lights
- Indicators
- Horn
- Radiator Fan
- Brake Light Switch
- Brake Fluid Level Switch
- Spare Wire for Future Turbo Boost Controller 🙂
- Thick Earth Wire
For most of this, initially, you are identifying where each of the wires needs to go, following the routing in the manual. Then extending each of the wires using the same coloured wire from your big box of spare wire – remember I told you in my last post to save a load! Insulate any joins well with a combination of heat shrink and wide electrical tape.
Use small bits of loom tape to hold the loom together and cable tie it to the saddle bushes to secure the loom. This is important to make sure the loom is the right length as you run it around the car. Once I’d done this, I started with the Headlights.
Rear Loom
The front to rear loom and the rear loom itself were both a pretty good fit for reaching most areas it needed to get to, with a few wires needing extending to allow it to reach the right hand side of the car for the rear lights.
Mounting ECU and Relays
I created custom brackets to mount the ECU and sat it on a small strip of rubber to stop vibrations. I also created a couple of custom brackets for all the relays. One of them was using a couple of the old MX-5 brackets cut apart and combined together in a slightly different configuration. This mounted the flasher unit and hidden behind is the immobiliser unit. I then created another relay bracket from scratch to hold the remainder. I also labelled all the relays with a label machine to help me fault find quicker later on.
OBDII Diagnostics Port and Charging
I decided I wanted the OBD port to be accessible from the inside of the car without having to open the bonnet. This would make it easier for diagnostics in general and also allow me to use OBD connections for screens, timing apps etc in the future more easily. So I created a small blanking plate for the relay cut out in the ECU mounting tray which I wasn’t using.
Next to this I cut out a small aperture to fit the trickle charge point for my Ctek battery charger that I had bought. Here is the final solution.
Covering the Looms
Once all the wires were at the correct lengths and all clipped back loosely to the saddle bushes, I then started to cover all of the looms and fix back for the final time.
I used the Braided Split Wire Loom Wrap for most of the loom and secured this in place with loom tape. This is great stuff to work with, provides a great protection and gives it a real professional finish, better than OEM in my opinion.
For the shorter off shoots on the loom to lighting connectors etc. I used the smaller braided wrap and with heat shrink on the end or loom tape. Here’s the final results.
I’m really pleased with the results. The loom is well protected and secured well and better than OEM. Now on to install the lights.
Summary of Build Costs and Hours
Here is a summary of the costs and person hours (total number of hours for every person that has helped) for the build so far. This should hopefully help others with the planning of their builds, by providing cost and time actually incurred for this build. A more detailed breakdown of all the costs and hours worked on the build to date can be viewed here.
| Person Hours Worked This Post | |
|---|---|
| Installation of Wiring Harness | 41 hrs |
| Car Build Costs This Post | |
|---|---|
| 3m Braided Split Wire Loom Wrap 20mm | £15 |
| 6m Braided Split Wire Loom Wrap 12mm | £28 |
| 3M Braided Split Wire Loom Wrap 8mm | £12 |
| 10M Braided Cable Sleeve 6mm | £10 |
| 10M Braided Cable Sleeve 4mm | £8 |
| Loom Tape 8x Rolls | £20 |
| Heat Shrink Tubing Assorted Set | £5 |
| 6.3mm Right Angled Spade Connectors 50 Pack | £5 |
| 100x Cable Ties 150mm x 3.6mm | £4 |
| Econoseal Automotive Connector 6-way Qty 1 | £4 |
| Econoseal Automotive Connector 2-way Qty 5 | £10 |
| M8 Cable Lug SC25-8 10 Pack | £6 |
| Totals | This Post | To Date | All Posts |
|---|---|---|---|
| Person Hours Worked | 41 hrs | 486 hrs | 486 hrs |
| Car Build | £127 | £13,514 | £13,514 |
| Tools / Consumables | £0 | £470 | £470 |
| Total Cost | £127 | £13,984 | £13,984 |