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I have the sheet metal done, suspension in, and differential installed. Before bringing in engine and trans, I'm working on the wiring harness. After removing wiring for radio, heater, air conditioning, power antenna, seat heaters, power windows, power door locks, air bags, pop-up headlights, seat belt warning chime, windshield wipers and washer fluid, I'm left with a significantly smaller rat's nest of wiring, but several wires going to the computer that are unidentified. Do I need the computer and mass air flow box to make the engine run, or can I just do a new hard-wire harness to starter, ignition, fuel pump, and lights and go with that? Mazda used very small-gauge wire for everything, and lots of relays everywhere to carry the "juice". Can I toss the computer and M.A.F. box and work from there?

Tim or should I say Grampa Tim. You're probably younger than me, so I'll just call you Tim.

You may want to start a build log with your first post starting it off. This gives everyone an understanding of who you are and what you're starting with.

Your previous post ----
Hello:
I have been a Lotus fan since the late 60s, and had an opportunity to purchase the last "North American" spec Europa off the line while stationed overseas. Laguna Blue metallic with the "oatmeal" interior and a ton of gold pinstriping. However, I was set to return to the Midwest, and at the time, the only Lotus stocking distributors were in New York, Baton Rouge, and Seattle. Regrettably, I decided to back out of the purchase, and walked away.
Fast forward 44 years, through marriage, jobs, kids, and businesses; and more boring vehicles than I care to remember.
At my retirement party, my amazing kids (and their equally amazing spouses) presented me with a Brunton Stalker 1962 Lotus 7 kit for Miata donor drivetrain.
After building a 10 x 20 shop, and prepping for and building our house, I've been spending a lot of time putting together my "car".
Looking forward to following the conversations, and posting some photos to share this journey.

Tim, in answer to your question you do need the ECU (computer) and the MAF sensor to make your Miata run. I would also save as many of the relays from the donor car and use them to make things a little easier. You can eliminate many of the fuses and relays based on your tossing out of the miscellaneous junk you already cut out.

What you may want to do is to get an electrical manual for your year of Miata and mark it up as you go as to what gets tossed and what gets kept. If I remember right, the Miata engine and electrical also has an immobilizer which will not allow you to start the engine without the key to match the ECU. What year is your engine? I may be able to help you further since I built a Miata Locost before my current Honda S2000 Locost.

Good luck,
Roy

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Build log http://www.locostusa.com/forums/viewtopic.php?t=16510

I do not have the key for the donor vehicle. am I going to be better off just doing the wiring I will need? Will I be able to run the engine without the computer and MAF unit?

The donor vehicle is an early 1990 - 1600cc.

Those parts are essential to the function of the fuel injection and ignition. There have been conversions to carburetors but you still need an aftermarket electronic ignition system but I'm guessing you just don't want to see these things under the hood?

You might consider doing all the fun stuff you want then paying someone to finish up the details including go over the whole thing. Don't throw away anything from the donor if you don't know what it is.

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Miata UBJ: ES-2074R('70s maz pickup)
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360LA 442E: 134.5x46x15
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Tim-
I think what everyone is trying to say is that you need to computer and MAF to operate the engine without major, major changes to the engine such as carbs and a separate ignition system. You could go to something like a Megasquirt type computer and accessories. If you're into electronics in a big way, Megasquirt might be for you. The computer needs to control the fuel injection and ignition, getting its many inputs from the mass air flow sensor, the crank sensor, the cam sensor, etc. etc. Without your donor key that makes it impossible to start the ignition because of the immobilizer, without some sort of an immobilizer bypass.

When you say you have an early 1900's Miata, exactly what year is it?

Again, good luck.
Roy

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Build log http://www.locostusa.com/forums/viewtopic.php?t=16510

Not having the key is okay, you'll need a wiring diagram but you will be able to bypass that fairly easy with some research. Echoing what others have said, you will need all the engine wiring intact, the engine will probably run speed density without the MAF but there is no reason to do that.

In my opinion, keep wiring around until you've test fired the engine, then start paring it down when you know everything works. A couple pounds of extra wire won't matter much as-is

Switching from fuel injection (compurerized) to carbs will reduce the wiring, but performance and reliability will both take a hit.

wiring diagrams can be found here: https://www.miataforumz.com/how-40/mazda-miata-wiring-diagrams-1990-2002-a-497/

Thanks for the info - looks like I have my work cut out for me