Hi all. I have mounted the battery in the hatch area of the car and my auto elec normally fixes the earth to the rear bumper bolt, which I am happy to do. Naturally i presume the best contact would be if I sand back the body around the bolt to bare metal before fixing the cable, ensuring the lug was in contact with the body. Having concerns with rust (as we all do) is there something I can spray/paint on the area beforehand that will protect it but not inhibit a good contact. Alternatively if I put washers between the cable lug before I fixed it to the bolt (so that it wasn't actually touching the body) will I get as good a contact? Thanks in advance. Cheers Ron
Earth Cable Body Prep Ideas
Posted 11 January 2021 - 09:54 AM
You are best off running a 0V cable of the same size as the +ve from the battery 0V terminal to the engine block. Plus a smaller one to a body connection in the boot, the same as what normally goes from the battery under the bonnet to the radiator support. I’d also run a smaller one from the engine 0V connection to the radiator support for the headlamps.
In the boot I’d find a spare captive nut somewhere in the boot area if there is one. Clean the thread out with a tap and use a new set screw with flat washer, preferably one with both captive spring and flat washers. Clean the surface under where the crimp lug will contact and use a conductive grease, lots around example below:
What I just described is the best way to treat the connection at the radiator support too. Also helps to do the engine block connection the same way. This way you get current through both sides of the crimp lug into the surface and also into the set screw then into the threads.
Even better conductive grease:
From memory copperkote works too.
Edited by yel327, 11 January 2021 - 09:57 AM.
Posted 11 January 2021 - 10:05 AM
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Posted 11 January 2021 - 10:37 AM
Posted 11 January 2021 - 11:49 AM
Thanks for the advice Yel and apologies. I've told you before my knowledge of cars is somewhat limited and this just proves it again lol. Is OV the same as -ve or does it mean over voltage or something else? I'm a bit stuck regarding running a second cable back to the engine as I have been guided by the auto elec doing the work and given my limited knowledge, don't want to second guess him, and he is a forum member and has done a lot of well known Toranas. I will take on board what you have said about it and in the meantime try to find the best place to fix to (without having to drill any more holes if I can help it) and use that grease. Car is due to be fired up for the first time next week so after that should/hopefully be able to identify any shortcomings with connections. Cheers Ron
Posted 11 January 2021 - 12:05 PM
I have 2 LJ track cars here at the moment.
Both have batteries in the boot.
One has the "earth" bolted to the rear bumper bolt.
The other has both 12v & 0v cables run from boot to front.
The White car with the bumper bolt was already done like that years ago.
I dont think any particular care was taken with the connection.
The Green car was wired all the way through with 2 cables.
i.e both cars have been wired as they are it for ages.
There is no difference in the way they behave.
( I did just up the cable sizes on the Green one, as I relocated the battery from inside passenger compartment to boot.)
As Byron said though, may as well use the good goo if you are starting from scratch.
Posted 11 January 2021 - 12:10 PM
Thanks Col. That gives me a lot of comfort. Is dielectric grease the same as conductive carbon grease. I ask because my local electric store suggests this as an alternative (also because I don't think they stock the carbon grease). Cheers Ron
Edited by Cook, 11 January 2021 - 12:14 PM.
Posted 11 January 2021 - 12:46 PM
To simplify things, it can be called a ground, instead of an earth.
They use different ISO symbols, so there is a difference.
Byron is right in saying that you should run a cable from both terminals up to the engine.
It may save some dramas electrically later on.
Tinplate is a reasonable conductor not a good one.
If you want to prepare a ground point on the chassis anyway, get out some solder, resin and a blow torch.
Clean up the area where the lug will be, then tin the spot. Make it larger than needed. ( that will likely happen anyway).
That will provide as good a connection as you can get.
Mask up the area where the lug will go and paint around it.
The tinned area wont rust.
Posted 11 January 2021 - 03:34 PM
Thanks Rob. This is sounding more and more like another one of those questions I should have asked before I had the car painted and all the driveline installed. Hopefully someone can make use of the knowledge. Cheers Ron
Posted 23 January 2021 - 11:32 AM
Attach to any body nut which is welded to the body or frame.
Make sure the thread and the bolt are clean and bare, rub some dielectric onto the bolt thread and attach.
The thread is ample for good ground connectivity. No need to scrape paint off the body.
Posted 24 January 2021 - 10:39 AM
Thanks Chris. I ground it to the bumper bolt after rubbing back a bit of paint inside and put some carbon conductive grease on before I fitted it on. Had some other issues but no dramas with the ground and finally got the car running for the first time in 9 years. Cheers Ron
Posted 24 January 2021 - 11:35 PM
finally got the car running for the first time in 9 years. Cheers Ron
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