Earth wiring

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oddknuds
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Earth wiring

Post by oddknuds » Tue Nov 29, 2016 9:57 am

I have a Scimitar 5a
From the battery negative pole is a fat wire that first connects to the chassi.
Then the fat wire continues into the engine compartment, but to where?
Can anyone tell me what this wire is connected to?

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Re: Earth wiring

Post by peter freeman » Tue Nov 29, 2016 10:00 am

Probably the engine.



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Dennis Nicholas
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Re: Earth wiring

Post by Dennis Nicholas » Tue Nov 29, 2016 10:28 am

Sometimes it goes to another chassis connection, down near the starter motor area, and then another wire or woven flexible connector from that point to the engine to earth the engine.......sometimes the starter fixing bolt is used, but anywhere with a good metal connection to the engine. Engine/gearbox is mounted on rubber mounts so isolated from chassis/earth and any electrical path is via ancillary connections such as choke cable, accelerator cable etc.......you can imagine what happens when big electric current for starter runs through say the choke cable........glowing red and melting actions.


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toomanysabres
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Re: Earth wiring

Post by toomanysabres » Tue Nov 29, 2016 10:45 am

I think originally the battery terminal went to a bolt on the forward extension triangle 'tinware'. This is a potential issue for starting since the current flow of the starter then has to go through the bolts holding that 'tinware' on thus an extra chance for rust/corrosion.
Its best directly onto the engine with a flexible (read welding) cable or to the main chassis lower down if a rigid wire type.


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Re: Earth wiring

Post by Dennis Nicholas » Tue Nov 29, 2016 12:41 pm

Maybe only 6 on had a lug welded to chassis down near starter? battery to forward earth lug then under same bolt head connector to engine would provide adequate surface connection between the two connectors
HOWEVER as said earthing from forward plate to chassis would be compromised by rust between plate and chassis.....however the connector from forward earth point back to chassis earth lug near starter (if it exists) would provide earth for chassis/rest of car.


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Re: Earth wiring

Post by toolmanchris » Tue Nov 29, 2016 12:56 pm

My 5a has a earth lug next to the starter with a heavy braid to the starter mounting bolts. It also has a heavy wire to the nose support crossmember at the front which I think this is the original layout.
I have added a large diameter wire from the front to a spare tapped hole on the engine block for good measure and I have no problem with starting at all.


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Re: Earth wiring

Post by scimjim » Tue Nov 29, 2016 1:20 pm

yep - standard is battery earth to front rail, then everything else is simply earthed direct to the chassis by braid or bolted direct.


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Re: Earth wiring

Post by scmarf » Tue Nov 29, 2016 1:44 pm

On Ben's SE5a the battery had been turned through 180 degrees by PO and an extra long positive cable fitted. This enabled an earth straight down to the front suspension chassis upright. It worked but we have reverted to the original arrangement with the earth going to the front tinware as 'toomanysabres' describes but in order to get around the issues of trying to earth through numerous dubious bolted joints, we put an off-the-shelf earth cable from the front bolt to the aforementioned upright. Worked fine but for the next rebuild we have a shiny new front crossmember. I think we will keep the earth cable as a backup though.

BTW, still need a standard positive cable (battery to starter solenoid) to replace the extra long one if anyone has one kicking about.


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Re: Earth wiring

Post by oddknuds » Wed Dec 07, 2016 3:37 pm

Thank you all for you valuable answers



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