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 Post subject: Ground management
PostPosted: February 1, 2020, 7:55 pm 
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Joined: January 27, 2010, 1:11 pm
Posts: 425
Location: Jefferson City, MO
I am trying to clean up my harness some. One of the issues is I have too many ring terminals on one stud for grounding. Any ideas on how to clean this up? I can ad another stud but dont want to add alot of extra studs. The only other option I can think of is to do a lot of splicing to combine them into fewer wires. Any other ideas? Under the scuttle I have a ground strip that I am using for my grounds but dont want to put a strip in the engine bay.

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 Post subject: Re: Ground management
PostPosted: February 2, 2020, 7:24 am 
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Joined: December 22, 2006, 2:05 pm
Posts: 6656
I found some really old pics of your wiring here: http://locostusa.com/forums/viewtopic.p ... &start=150

I’d move all the grounds to the top rail with a 1/8x1x1 or 2 inch strip, within a foot of four or more components, pre-drilled, vertical and welded on two sides. I use ¼-20 bolts bolted to the tab, then a washer, eyes, washer, lock washer, nut. I think they are 1-1/4 long.

Another, cleaner option is to drill a hole in the center of the tube, weld a nut over the hole, chase the threads, then bolt the grounds to the rail directly. Then you will never stab yourself on protruding threads and the bolt is less likely to corrode inside the top rail.

For the relays, when you weld a strip to mount them, make it a couple inches longer to provide a ground stud on the end and a small hole to zip tie the loom.

I’d move the engine ground to within a foot of where it attaches near the engine mount, then weld a tab to the frame side of the engine mount to bolt it on and solder the ends.

Wiring, including grounds, should be above any liquids that can soak them and soften the insulation or corrode the wire.

Ground tabs should be easily accessible for tools and cleaning but not draw blood on the mech trying to work on something else.

It is better to have a single purpose ground attachment versus also holding a bracket to the vehicle so they don’t get disturbed/flexed from unrelated service. It makes sense for retrofit but not a preferred practice.

The chassis is a negative bus bar. Ground points should be close to the component to reduce volt drop, wiring, cleaner install, and less weight.

The battery cables look to thin for this application. They should be in a gauge appropriate to the cca requirements for the donor vehicle. I’d go 4-6ga with short cables for a miata drivetrain. It looks like you have a 6ga for the engine ground to chassis but the bat cables look really thin in the pics of when it was not finished. I crimp in a vice and solder the eyes then heat shrink. When buying cable, beware “copper plated” in the fine print.

My sunroof has been leaking on the 4.3l fiero. Rotted my Mr. Mikes leather seats :BH: but they are about 20 years old now. Another forever project I need to get back to. I never should have retrofit a sunroof roof. :ack:

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 Post subject: Re: Ground management
PostPosted: February 2, 2020, 12:49 pm 
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Joined: April 23, 2006, 8:26 pm
Posts: 6046
Location: SoCal
As an EE, grounding causes more problems than just about anything else. In a car, it's less important to have separate power and signal grounds (though there are exceptions for some low-level ECU signals). It comes down to a bit of a "pick your poison" in your case. You can have one stud and put them all on it, with the understanding that if it ever gets loose, everything's going to go bonkers at the same time. I've used strips of copper, with separate returns for every signals, and the strip connects to the chassis through its mounts. Personally, I'd veer more towards functionality over appearance. If you don't like the looks, hide them under something; good grounding is too important to put appearance over function.

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 Post subject: Re: Ground management
PostPosted: February 2, 2020, 1:20 pm 
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Joined: July 17, 2008, 9:11 am
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Location: West Chicago,IL
My mantra is: Engine and ECU sensor grounds that are grounded on the engine should be to a single point on the engine. Then a heavy cable 4GA or larger, should run to the chassis as short as reasonably possible. If the battery is located anywhere near that, it should be grounded close, but on a separate stud. Any other grounds that are electrical in nature, rather than electronic, can be grounded virtually anywhere. i.e. lights gets grounded near their sockets, cooling fans get grounded near the fan, relays also grounded near them, etc.

I see a lot of excessive loops of wire in your single ground. I would shorten them leaving enough wire for cutting and re-terminating in the future, a "service loop". To address this Gordian knot of wires, I would separate the battery grounding wire to its own stud/bolt. Then put 2 wires each to their own ground screws, certainly no more than 3. Whether you bolt directly to the tube or weld on a tab and bolt to that, is personal preference IMO. But.....if everything is running well the way it is, I would not make any major change your grounding scheme to quickly. No need to introduce grounding issues by changing the grounding locations.

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 Post subject: Re: Ground management
PostPosted: February 2, 2020, 4:01 pm 
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Joined: June 20, 2019, 12:34 pm
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This is something I have a lot of experience with. In hospital equipment, grounds can carry "eddy currents" caused by ground loops. If too many loops are created you can end up with noise and a shock hazard (but on a car- no real shock risk). On older simple electrical systems on cars the noise is of no consequence. But with modern electronic controls and microprocessors you can end up with interference and problems.

Try to keep the number of ground points to a minimum. Make sure the stud mount(s) are secure and all paint is removed to attached frame. The ground wire from the battery to the frame should be at least the size of the positive battery lead. And make sure the engine block is well grounded to the frame.

Any EFI, CDI or ECM control boxes must be well grounded or you will experience unusual problems that seem to come and go. And as MV8 pointed out, make sure your crimps are secure. Many a ground has failed due corrosion or an improper crimps. Most failures attributed to Lucas is really due to bad connections and corroded crimps.

Thom


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