TLDR: After YEARS of dealing with this I finally am putting myself on front-street...Probably 15 years ago my car developed a hit-or-miss starting problem; I would turn the key and sometimes the car would start, sometimes it wouldn't. At the time I thought it was the main relay being "temperamental" so I went through a series of suggested fixes until I landed on replacing that relay with some heavy gauge wires leading to a switch in the cockpit and I became the main relay. That was my setup for a while until I replaced the stock relay with a HD one from FM and that worked like a charm. Until...

The car refused to start at all with the key. All I would get was a single click and...nothing. The car would crank just fine with a jump box, but I didn't want to deal with that forever. So I decided to boost the starting output with a dual-battery setup. I installed a lawnmower battery in the left well of the trunk and wired it through a "Battery Doctor" (battery isolator) that would allow both batteries to be charged when the car was running but would only allow one battery to feed the starter normally UNLESS I pressed a button on the Battery Doctor which would feed both batteries to the starter. That worked sometimes, and sometimes it wouldn't.

At that point I found that there was some kind of parasitic drain that would partially drain the main battery overnight and the other battery wasn't strong enough to turn over the car by itself. So, I installed a kill switch to disconnect the battery ground (thus making that parasitic drain irrelevant), and installed two ports (one on either side of the car where I could plug in two trickle chargers to keep both batteries charged overnight while they were disconnected from the rest of the car. But that did not solve the "sometime start, sometimes not" problem.

Then I thought "maybe it's the ignition switch itself that's the problem". So I installed a Start Button in the center console and a relay under the dash so that the only thing that the key does now is enable all of the car's circuits EXCEPT the starting circuit. That happens by pressing the Start Button. The end result...no difference.

SO...I replaced the starter (with a reman) and wired in some heavy gauge wires; one to the starter and the other to the ground in the trunk and put in a plug so that I can plug in a jump box from the cockpit and start the car. So, my starting sequence is; disconnect the chargers, turn on the kill switch, turn the ignition key, plug in the jump box, put it in "Start" mode, press the Start Button, turn off the jump box and drive into the sunset.

The crux of the matter
I said all of that to say this...WTF is WRONG with my electrical system that I can't start the car without a jump box?!! I have a 2 year-old (reman) starter, two freaking batteries that charge up to 12+ volts EVERY NIGHT, an "isolated" starting circuit, a HD main relay (that doesn't get hot like the stock one did) and 80% of the time the damned thing will NOT start without a jump box assist.

I'll keep doing what I'm doing, but the whole "pre-flight checklist" thing has gotten old.

PS - I HATE automotive electrical systems!

 

Check your clutch over-ride switch. I chased a chronic no-start issue with my '93 for years, changing starters multiple times, adding relays, replacing the ignition switch and completely rewiring the circuit from the battery to the starter. Turns out it was the switch on the clutch, which had become intermittent. With that bypassed, I had arguably the most reliable starting system of any Miata, ever.

 

My clutch override switch "left the building" a LONG time ago. I had that metal clip that FM sold on it for years and a while ago it was deleted altogether.

I appreciate the input never the less!

 

I go a PM from @technicalninja to check the ground cable to the PPF. That's one thing that I have not touched in all of this time of ownership. He suggested a "quick-and-dirty" test using a jumper cable from a bolt on the starter, to the negative post of the battery. Well, I did that this morning with a janky jumper cable that was in sad shape and lo-and-behold, the car started (albeit struggling a bit) with the single battery!

So, my next step will be to get a length of zero-gauge wire that I have laying around, and ground the starter bolt directly to the negative battery post (or, maybe to the body ground in the trunk) and see what transpires.

Now...someone tell me why that might be a bad idea...

 

Not necessarily a bad idea, but probably overkill and unnecessary. 0 gauge wire is a lot, the run from the battery to the starter is pretty huge, and you're addressing the symptom rather than the cause.

You've got a bad ground somewhere.

What I'd say is to go back to that jumper cable, attach one end to the negative terminal of the battery, and try some different locations with the other end.

• Body - if this connection fixes the problem, you have a bad ground between the battery and the body, in the trunk.
• Engine block - if this connection fixes the problem, you have a bad ground between the engine and the body, probably the woven metal strap under the brake booster.

HTH

 

Well, I thought I had enough of that 0 AWG to get from the battery to the starter, but I was a few inches short (how many times have I heard THAT?!!). I have some 10AWG wire laying around, but I ran out of incentive on Sunday.
I will try your tips, but I think you're on the right track.

 

Okay, just to follow up on this and to ask another question...

This is related although I don't know how. I had a situation where my cooling fans were not working as expected. I had them wired in parallel through the connection(s) to the ECU for the cooling and A/C fans. In addition, I had a switch on my console so that I could activate the fans on demand. The problem was, that in the RUN position, the fans wouldn't turn on, but in the ACC position, both fans would come on just fine.

So, I spent all weekend trying to figure out WTF was going on - why weren't the fans turning on when the key was in the RUN position. After hours of searching through wiring diagrams and pouring over my sloppy wiring. Anyway, I found out what the problem was...instead of having the switch wired to ground (which would technically activate the two fans), I had the switch wired to 12V...don't ask, I don't know how, or why that was.

ANYWAY, once I corrected that, my switch now activates the two fans in parallel with the key in the RUN and ACC positions. BUT as a side-effect, I can now start the engine with the key in the ST position (actually, it's through a BRB [Big Red Button] on the console - but that's a technicality). So far, for two days now, I can actually start the engine without a jump box!!

I am NOT an EE, so I can't explain why this is, but all I can say is that (so far) I am jump box-less!! Anyone that wants to jump in with an explanation is welcome to provide an answer.