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Giant black wire coming through firewall ! Where do it go ??

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Ok guys - 71 2dr, trying to figure out wiring.  Have a very large (4 ga ?) rubberized black wire coming through the firewall with a lug on the end.  It's maybe 2 feet long.  Can't figure out from the wiring diagram what it attaches to the engine compartment (it's not the negative battery terminal).   Also don't know where it goes on the other side of the firewall.  Is this stock ??  What is it and where should it terminate ?   Thanks all -

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Where is this wire coming through the fire wall? At or with the regular wire harness near the starter????


Black is Nissan ground color code. Move the wire around and see where it reaches to. Maybe something obvious that was disconnected.

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Electrical "lug" at the end?  If you mean a NUT at the end, maybe the car had an aftermarket oil pressure gauge at some point, it might be a capillary tube for the oil from the engine to the gauge (now missing??).  There are no large gauge black "wires" going THRU the firewall on its own, on a 1971 510............all of the black GROUND wires were inside the main harness & poked out when used as a ground or to attach to something electrical.

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On 1/18/2022 at 3:49 PM, Logical1 said:

Cable Lug:





Understand some use that terminology..............was trying to get him to clarify, cuz again, there are no large black wires going thru the firewall individually, from the factory! 😁

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  • 2 months later...

I'm sure everyone was holding their breath for the outcome to this one (sarcasm intended).  I determined that this was a #2 welding cable (with a rubber sheath), put in by the PO to handle a trunk-mounted battery.  It had been cut short in the trunk and I didn't notice it until I went to remove the fuel tank.  The lug in the engine bay was disconnected, but was meant for the starter terminal.  So I extended it in the trunk, put in a battery mount, and now have a working trunk mounted battery.  It comes through the firewall with the rest of the wire harness, and that's what was confusing me - plus it's huge and has that weird rubber insulation.  Anyway, it works and mystery solved.  Thanks for the input !

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