Catastrophic Electrical Short
 

I was installing my friend's clutch on his 92 miata when I moved the starter and accidentally pressed the wire (the heavy gauge one) on some bracket bolted to the engine. Obviously it sparked, so I tried to move it away but it didn't seem to help. I ran to the battery and disconnected the positive terminal, but by that time there was smoke everywhere.

I know I screwed up. I've done dozens of clutch installs with no problems, but that is no excuse not to disconnect the battery.
At this point though I really need advice:
What should I expect in terms of damage?
What should I be doing for troubleshooting and whatnot?

Any input can help, thanks

you just did a little welding...

the smoke may be the positive wire getting too hot. if the insulation on the wire is gone, i would just run a new wire.
otherwise, it may still be ok.
but as you say, if it took you to get out from under the car, get up, run to the turnk, open, get a 10mm and disocnenct the negative...you toasted that wire.
just replace it.
nothing else should've been broken.

Most likely, yes, the insulation on the positive battery wire has been damaged. If it were my car, I'd re-run the whole wire from the battery to the starter, to lessen the risk of the damaged insulation causing a short circuit while your friend is driving down the road in in the future. It's a bit of a pain in the ass to access in some places, but it's the only safe bet.

This wire runs under the car, through a plastic channel attached to the PPF. It's the path highlighted in blue:

https://www.miataturbo.net/attachmen...1&d=1405695133

While you're down there, inspect the other wires that also run through that channel. If you're lucky, the battery cable didn't melt any of the other wires next to it.

Protip: once you remove the old battery cable, take it to a diesel truck shop or a *COMPETENT* car stereo place and have them make you a new one with properly crimped connectors. You do not have the correct tool to put on the starter-side ring connector properly.

Also, don't forget to inspect the three ground straps- one from engine to body on the exhaust side, one from PPF to body under the car near the diff, and one from body to battery. It's possible that these may have been damaged as well.



You just learned a valuable lesson. I learned the same lesson on a '71 VW, when I welded a Craftsman socket-wrench to the body of the car. After I chiseled it loose, Sears replaced it for free.

I did this to my oil cooler lines recently, the SS sleeve is still welded together, but holding fluid fine :)

I also have the above blue shaded harness from the MSM I'm parting out if you'd like it. It includes the fuse box with the main relay/fuse of course, but I think it's mostly the same between years, although you could just swap the fuse box.

Actually, I think I do have the correct tool to crimp the starter-side ring terminal:
https://www.miataturbo.net/attachmen...ine=1405705044
Any reason this wouldn't work? I could pick up some ring terminals from McMaster and use this to crimp them.

I also have a bunch of 4 gauge amp wiring, and I think a friend of mine has some stranded wire from home depot (not sure what it's meant to be used for but the strands are fairly thick). Would either of these work? Not trying to cut corners here, but if what I have available to me is sufficient, obviously I'd rather save the money. If not though, I might hit you up for that harness, curly

Thanks for the input guys, helps a lot.

It's worth a try, I guess. I've only ever used this style: Mechanical Indent Crimp Tool, 8 Ga. - 250 MCM



Thick strands is usually a no-no for applications where the cable is going to be subjected to a lot of movement / vibration.

So-called welding cable is often used in this sort of application. It generally uses very fine strands (30-32 AWG). I honestly have no idea what the internal construction of the OEM cable is- I've never needed to cut one apart.

You'll probably need to replace the battery too.

Don't panic just yet. Automotive wiring harnesses tend to be pretty tough and durable unless you just really overload them. Start by stripping back the harness covering from the location of the arc. If you don't see melted plastic after the first 6 inches or so, you probably haven't got a major harness problem. Check all the fuses under the hood plus those under the dash and then begin checking for shorts, using a multimeter. The White/red wire is a good starting point, since it is a main distribution path. Grab a copy of the wiring diagrams for your year model to guide your multimeter tests.

I had a pretty serious magic smoke release, involving the main engine harness on my 95. I figured I was screwed, just as you are feeling now. I had to replace 4 fuses to renew the magic smoke, but the harness survived the event without a melt down. It cooked a coil and the CAS was toast. Other than a nasty intermittent pin connection inside the CAS plug, the harness was fine.

That will work. I use a Hobart version of that to do the crimps on the 100A DC feeds in our data centers. Haven't burned anything down yet.