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I've been largely ignoring my ground wires up until now, both when I was stripping down the harness and when installing/modifying the harness to suit the Seven. I've got all the colored wiring (wires of color?) done (yeah, right!) and am now focusing on the black wires.

I welded a tab with two bolts to the frame under the scuttle, and mounted the two "ground junction blocks" there. (I made up that term...the piece with five black wires coming out and a tab to bolt it to the frame.) Then I just run all the black wires from various components to one of the wires. For components with tiny 18 (20?) gauge ground wires, I might combine two into one of the junction block wires, but for the most part every component gets its own wire...there is no shortage!





I have three questions/concerns:

1. Where does the battery ground strap connect to the engine? I suppose it doesn't matter too much, but I'd rather stick with the stock location to be on the safe side. I expected it to be on the block, but I don't see any obvious places where it was. I found some references to the back of the head, but couldn't find any precise references, and again, no evidence. I suspect this one, lonely bolt on the right side of the bell housing, but I really would not expect it to be on the tranny. FWIW, this is a '93 Miata.





2. There is one large ground wire with an eyelet terminal at both ends. I think it's around a 12 gauge wire. It's about 4 feet long, and has some other grounds tapping into it. Does this wire go somewhere critical, or is it just a big, fat ground trunk for other circuits?





3. On the engine harness, I put all the grounds under one bolt. This includes the black grounds, and the black/green grounds. I think this is a mistake, and would like some feedback. I'm concerned that the black/green grounds are signal grounds (right?) and that voltage from the regular grounds might overwhelm the signals. Is that a valid concern? If so, how isolated should they be? Regrettably, I don't have photos of this section prior to my changes, and haven't found photos of this online.




Thanks in advance for any tasteful replies.
-dave

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...nowadays people are so intellectually lazy and lethargic that they can't build ANYTHING with their hands. They'll spend hours watching whiny people marooned on an island, but won't spend a second adding anything to the world. -weconway
Visit my [Locost 7 build log]

Dave,
The grounds are no problem. I will swing by tomorrow if you are going to be around and spend a bit with you on the electrics.

Gene

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1987 Fiero Caddy V-8 Powered
1994 Vulcan 1500 2 wheeler
SHO Powered Locost coming to a street near you Summer 2009 uhh 2012/2013????.
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It sounds like your doing the right things. I think the important things with the grounds is that they connect directly to the chassis and avoid any "daisy chaining" with the signal grounds. Especially on heavy ground wires that carry current.

The best thing would be to look in a car at a salvage yard, but it looks like Scrabblegod will be a help there..

You can see that the Turkey must have been carrying a substantial current, from the color. Stick a fork in it, it's done. Generally it's probably better to pass the current from side to side, rather then end to end - otherwise the ends might over cook and fail before the rest is ready. Good luck!

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Marcus Barrow - Car9 an open design community supported sports car for home builders!
SketchUp collection for LocostUSA: "Dream it, Build it, Drive it!"
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The ground bolt is on the drivers side of the head, about an inch up and to the right (toward firewall) of the exhaust manifold.

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New owner of the formerly Winston's, formerly Stein's, Miata-Based Locost Build.

This is my plans (they are similar to the stock). Im going to ground the battery to the chassis as close as possible to the battery. The engine itself will get grounded to the chassis near the "factory" location. This is a wire braid (not plastic shielded) from the back of the head to the frame rail area under the brake stuff. For the 7, this wire will be grounded to the chassis as close as possible.

One word of advice, look up the write up on the FM site for the 90-93 LINK ECU install. There is a small part on improving the grounding for the ECU itself. It's been shown to help even stock ECUs behave better. I believe you cut a ground wire at the ECU and splice in a wire to the back of the head (the one I talked about above).

Thanks, guys! The Flyin' Miata page was quite helpful: http://www.flyinmiata.com/support/instr ... lation.pdf

It was a bit surprising to see they moved the signal ground to the same place as the main engine ground strap. I guess that pretty well abates my concern about having the signal ground tied to the other grounds.

-dave

ps. See you soon, Gene!

_________________
...nowadays people are so intellectually lazy and lethargic that they can't build ANYTHING with their hands. They'll spend hours watching whiny people marooned on an island, but won't spend a second adding anything to the world. -weconway
Visit my [Locost 7 build log]

They may have found an improvement just because they moved the connection, more then where. If you want good grounds for signals with low currents, you need gas tight connections to prevent corrosion. This is what good crimping or good soldering gets you.

_________________
Marcus Barrow - Car9 an open design community supported sports car for home builders!
SketchUp collection for LocostUSA: "Dream it, Build it, Drive it!"
Car9 Roadster information - models, drawings, resources etc.