What needs to be earthed?

[xb-60]

Starting to look at some of the smaller detail items on the “to do” list for my 289FIA replica build.

Any detail descriptions and advice on items that need to be grounded/earthed would be much appreciated.

Relevant information that might be different to the average build:
• The chassis is a semi-monocoque unit that is all aluminium alloy, not mild steel

Here are some of the items that I’m aware of that would probably need attention, but feel free to expand further (I’ve not built a car almost from scratch previously)
• Fuel tank (mine’s aluminium alloy)
• Fuel filler (any detail I need to pay attention to?)
• Engine (302W, so cast iron) - needs earthing to alloy chassis?
• Gearbox (Toploader, also cast iron) -needs earthing to alloy chassis?
• Radiator (alum. Alloy) to alloy chassis
• Radiator ….Mg sacrificial anode on the cap, as well? Yes?
• Wiring? I'm a mech. eng. ....wiring is not my strong point

Anything else? A little care and attention now might well save wasted time and cash further down the track, so all comments welcome…

Thanks in advance.

Cheers!
Glen

[1795]

Glen,

I am not entirely sure about the influence of the alloy chassis, but for my car the battery, starter motor, engine, electric fuel pump, MSD box and at least some, if not all, of the dash instruments are grounded. The Toploader does not need to be grounded.

Jim

[patrickt]

This is the tried and true method of grounding:

Negative Battery Terminal to both frame and engine (block or cylinder head)
Opposite Side Cylinder Head to frame
Intake Manifold to firewall
Transmission to Frame (because ground current will go through the transmission bearings)
Gas tank and fuel inlet to frame
MSD boxes and under dash wiring should have a dedicated ground

[spdbrake]

I'd get a book on Galvanic corrosion (dissimilar metals) and study the standard practices. EX: Alum washer under the head of a steel bolt where it contacts an Aluminum surface. Prevents the Aluminum surface (Anode)from pitting and the washer is sacrificial.
A quick version.
https://www.assda.asn.au/technical-i...etal-corrosion
A bit more info.
https://www.faa.gov/documentLibrary/...r/AC_43-4B.pdf
And from the experts. Navair 01-1A-509-1 is the introduction to corrosion manual.
https://www.nsncenter.com/Library/TM/TM-1-1500-344-23-1

[patrickt]

Remember that your car is just sitting 99.9% of the time, so make it really easy to disconnect your battery so there's no sort of goofy barely measurable potential difference that will, over a couple of decades, eat away at something that you can't see. I like a simple knife switch. Even our friends from down under can handle that, unless they drop a spanner on it.

[Blas]

You could just use the wiring diagram from another manufacturer as a guide for the wiring and grounding. Consider making 1 or 2 specific grounding station lugs under the dash. One in the trunk and two under the hood. Remember to remove the chassis paint at the grounding points on the chassis and always add a star washer on the bolt connection. Always attach a large ground to one of the bolts on the starter. What you want to prevent is grounding thru the radiator and coolant. (Does not need to be as heavy a gage as power to starter because of short length of ground wire)
Buy a good tool for installing brass wire connectors with full insulating covers on the connectors, not those hardware store pinch connectors. Use shrink tubing at the connection of wire and connector. (all the same length) When harnesses are finalized, add non- shrink tubing or use self-vulcanizing electrical tape on the looms to prevent chafing. Rubber grommets where wire passes thru metal of fiberglass. Look into the different kinds of master kill switches. Using a knife switch as suggested, will not shut off a running car, and if used, can send a spike thru the cars electrical system when current flow changes from battery to alternator source. Do some research on the cut-off switches available, unless you only want a battery disconnect version.
Relays (with plug-in bases) should be used for all high power users (horn, fuel pump, fans, and headlights) and consider not using the single DIN127 single relay for low and height beam headlights. Split into two standard relays - one for low and one for high. Each fan should have a separate relay if you run two fans. And kick-up the wire gauge on the headlight wiring, you will get better results with illumination.
Blas

[patrickt]

The biggest deal is that you make sure all your connections are tight and clean. Your crimps need to be fresh, firm and preferably soldered as well. Always scrape to bare metal and use a quality electric contact cleaner like trichloroethane if they let you use that down there. If not, use whatever contact cleaner you can buy. The poisonous stuff always works better than the safe stuff. And always, always, always put a coat of dielectric grease on your connections. It is God's gift to electricity. Now, if you Google it, you will find stupid people saying "why would I possibly put a dielectric compound between connectors? Dielectric means it doesn't conduct, so that's like putting a sheet of rubber between my connectors." Those are the same people that swore the earth was flat because they couldn't see the curve of the earth from their windows. Under a microscope, perfectly flat connectors look like the Swiss Alps, and only the peaks are touching one another when two flat connectors are fastened. Dielectric grease fills the voids on "flat" connections and prevents degradation of the connection. There's only a million studies out there that confirm its wonders. Use it. Always. Everywhere.

[Gaz64]

Originally Posted by patrickt

The biggest deal is that you make sure all your connections are tight and clean. Your crimps need to be fresh, firm and preferably soldered as well. Always scrape to bare metal and use a quality electric contact cleaner like trichloroethane if they let you use that down there. If not, use whatever contact cleaner you can buy. The poisonous stuff always works better than the safe stuff. And always, always, always put a coat of dielectric grease on your connections. It is God's gift to electricity. Now, if you Google it, you will find stupid people saying "why would I possibly put a dielectric compound between connectors? Dielectric means it doesn't conduct, so that's like putting a sheet of rubber between my connectors." Those are the same people that swore the earth was flat because they couldn't see the curve of the earth from their windows. Under a microscope, perfectly flat connectors look like the Swiss Alps, and only the peaks are touching one another when two flat connectors are fastened. Dielectric grease fills the voids on "flat" connections and prevents degradation of the connection. There's only a million studies out there that confirm its wonders. Use it. Always. Everywhere.

Exactly correct. Helps to prevent fretting corrosion. I use it on any connector that is critical for low voltage signal loss, especially electronic throttle control circuit wiring.

[patrickt]

Originally Posted by patrickt

Those are the same people that swore the earth was flat because they couldn't see the curve of the earth from their windows.

And they're the same people that think your oil has to get to 212 degrees Fahrenheit to get moisture out.

[xb-60]

Thanks for the comments and advice.
I have some professional knowledge in, and expertise with, galvanic corrosion. What I really need - and have largely obtained (thanks!) – are tips and tricks, and safety aspects, specific to Cobras .…things like the need for earthing the fuel filler, even though there is no metal-to-metal contact there, aside from the mounting screws/nuts/washers.

Cheers!
Glen

[xb-60]

Originally Posted by 1795

Glen,

....at least some, if not all, of the dash instruments are grounded. The Toploader does not need to be grounded.

Jim

Jim, if the only electrical connection to most of my gauges (oil pressure, oil temp, coolant temp, speedometer) is for lighting, do they need to be grounded to the chassis?

[1795]

Glen,

Mine are grounded to the forward hoop in two locations and the only electricity is for the instrument lights.

Jim

[xb-60]

Thanks all. Comments duly noted and added to my build documentation.

Cheers
Glen

[kitcarbp]

If your charging system is using and old school external voltage regulator make sure it is grounded correctly, not mounted on thick paint that is not providing adequate ground, solved by removing a little bit of paint beneath the mounting bolts on the regulator housing or running a separate ground wire from reg housing to a known good ground.