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Electrical:

To some this is the most daunting part of the swap but I was excited to get into it; I don’t mind doing electrical and having chosen the simpler OBD1 version of the Miata was less intimidating.  It took time, but was a blast.

 

I’ve put together some basic stuff here and hope to get back at it with more details and better descriptions.  Hopefully this will be of some help though.

Please keep in mind my “proof of concept” attitude and the fact I really just wanted this thing on the road so again, nothing is pretty.

 

Throughout this section some of the images will look like an absolute mess, but it’s like anything, just take it a bit at a time and you can easily figure it out.

 

Most guys I read have done basically a 2-part electrical system.  Keeping the domestics on the old Spitfire Fuse Box and routing and adding the Miata Main Relay Box somewhere else in the car.  This is a great idea to get things going and it’s proven.  One day I’ll likely add a different Domestic set-up with modern blade fuses, but for now this works.

Planning

 

Before pulling any wires out of my donor car I wanted to make sure I didn’t cut or damage anything important so I put my plan together first (in the end not a big deal as I pulled all the wire out unharmed).

 

I printed out all the wiring diagrams from my Miata Factory Shop Manual and taped them together in a way that was sort of logical and easily connected (for me anyway).  Then I proceeded to draw/connect each line/wire as they are in the car.  This taught me tonnes right out of the gate but I did go through a bit of “Concentration Fluid”.

Wiring Diagram

 

I determined what I needed and what I didn’t and created my first Wiring Diagram on easel paper.  That’s what I put up in the garage as I wired it all up.

Things I decided I did NOT need or initially care for were...

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  • Clutch Switch and Neutral Safety Switch

    • The Spit didn’t have these and I was fine like that

    • Also, the Clutch Switch was fairly robust and had big current going through it

    • So, simpler, safer (electrically anyway) without it

  • Direct Power to ECU

    • this part of my ECU was actually damaged from rust/short.  I later picked up another ECU and will install that at some point

    • At that time I will add a “Check Engine” light and this "12V in" as well as I think it was for the ECU to retain OBD Fault Codes.

  • Brake Light Switch – I think to let the ECU know that it can allow RPM to drop at will to help with engine braking

  • Air conditioning Relay Input

  • Power Steering Input

  • Heater Control Unit (x2)

  • Combination Switch (lighting)

 

I believe the last four were basically Idle Control Features, that is, when selected the ECU would compensate Idle RPM so it didn’t drop.  So far no issues without them.

With Plan in Place

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After all the planning I carefully labelled and pulled the harnesses out of the Donor.

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Cleaned it up as best I could and removed any protective coverings, rigid bend supports, and fasteners.

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I put it all on the Dining Room table and went at it.

Another Temporary Measure

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I really wasn’t 100% sure that the locations I’d chosen for the Relay Box, ECU, Circuit Opening Relay, and Diagnostic Port were my final choices so I left most of the wire that was part of these systems intact.  That of course leaves a bunch of wire to stow.

 

The good part is that all of the wires were long enough to do it that way and I didn’t have to splice anything in.  Best part about that is that all the Miata colour coding remained.

Bad part is that I did have to stow it and it will need to be cleaned up.  When I get back at it, I’ll clean it all up and cut out the extra crap.

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I looked at mounting the ECU on the firewall, but decided it may be damaged by a passenger.  Up onto the back of the Battery Box should be a little more safe.

ECU Mounting Bracket

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I wanted to the ECU to be secured well, but to get a screw driver or wrench up high behind the dash when it was completely assembled would have been a challenge so I made a two-part bracket.

The upper part was just an “L” that slid under a bit I bolted to the back of the inside of the battery box.

The Lower part was just bent metal that could be removed from the back of the battery box, or from the ECU itself; easily accessed bolts.  Likely could have just done the lower one with some other tabs up top, but it’s done now.

Mostly Sorted

 

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Sort of Tucked Away (for now)

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​Also visible here is the bracket

holding the ECU in place.

Other Components

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The other boxes were just secured to the side portion with bolts protruding out where the bonnet latches.  An ideal set-up would have all of the components on one board that could be disconnected and removed.  A single, or a few connectors added here would make for easy disassembly and servicing.

Into the Engine Bay

 

I managed to get all of the engine wiring out through the right side of the battery box with a grommet I cut from an old Prelude parts car and then up the right side of the engine.  I used a fuel hose with a cut along its length to protect the wires as they turned forward out of the battery box.

 

Eventually when I get the domestic wire redone I’ll try to get that out the right side of the engine as well.  Might be a bit more wire, but will really clean up the other side.

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             Coming through the Battery Box                                                   Under the Intake                                                    Crossing Under the Front

Gauges

 

Man, I had dreamt that I could gut the Miata gauge cluster and somehow fit the internals to some old Spit gauges to keep the stock look, but, although it could work, I wasn’t prepared to do all the cutting, redoing PC Boards and lighting, so I decided to skip it.  For now I just added some wire and put the Miata cluster on the floor in front of the passenger seat.  It’s just for oil pressure and engine temp so I can live with it like that for a bit.

I’ve always wanted SpeedHut gauges anyway! :)

 

I still have the Parking Brake Light (no PWDA) and Fuel Gauge working in the original dash.

The Opening Circuit Relay and Fuel Pump

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Pretty straight forward when you look at it.  I put the Fuel Pump in the trunk/boot, so needed to run wire back there.

Dual Electrical System (as mentioned above)

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To tap into the Domestic power for some of the engine functions, specifically to feed the Miata Relay Box I put together a little connector segment.

I came up with this idea earlier when designing my Push-Button Start System (that will also come later).

Instead of cutting and splicing into existing wire I purchased a new 9-place Ignition Connector (male and female) and used that little bit as a place to tap into.  Just pulled apart the existing Ignition Connector and put this in between.

Schematic Diagram

 

Putting this together took longer than doing the Engine Swap, but here it is.

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Eventually I'd like to draw up a Wiring Diagram like the excellent one for the Spit mentioned earlier on this site, but for now this will have to do.

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