JT-130-hcpu
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Nearest earth point?
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300bhp/ton
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Everywhere... moderns cars are negative Earth 
Tenebreaux
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Yeah, that confused me. My answer would have been, "anywhere you can bolt into bare metal".Everywhere... moderns cars are negative Earth
Litch
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Or you could just run a dedicated earth back to the battery or main earth point, saves any problems in the future.
I have just rebuilt my 90 on a new chassis and don't use the chassis or bodywork for earthing at all.
I have just rebuilt my 90 on a new chassis and don't use the chassis or bodywork for earthing at all.
300bhp/ton
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Not being mean. But doesn’t represent a lack of understanding in how the system works?
Litch
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Not in the slightest.
What do we do when we put our LR's together? We try to isolate the different metals as far as possible to avoid corrosion.
We make sure all surfaces are painted, use rubber / plastic / nylon gaskets where alloy bolts to steel, use nylon washers to insulate the steel washer from the alloy, use grease to act not only as an anti-seize lubricant but also as an additional isolating layer etc etc. Having done all this good work it is very likely that there will still be metal to metal contact at multiple locations and you could probably get away with (for example) relying on a self-tapper into the rear tub to provide an earth to the rear lights but it is not perfect and we have all seen the white powder corrosion that forms in time. How many queries are there on this and other forums where the first answer is to "check your earth" or alternatively "why is my handbrake cable smoking"?
Of course you could get past this by making sure that you clean all the paint off the mating surfaces before bolting the body together and making sure that the bolts make a good metal to metal contact but then you have deliberately gone and created what we try to avoid.
Likewise the chassis, we try to rust-proof the steel chassis with paint / underseal / zinc etc but then go out of our way to create a metal to metal contact in what is usually one of the areas most susceptible to road salt & muck.
The easiest solution is not to rely on the body or chassis to provide the earth and instead run separate earths to the various earth points around the vehicle (there aren't actually than many), easy to do and as long as you make the terminations secure then you will have a reliable set-up and the beauty is that if you ever do have a problem you only have to check the earth points, not go chasing possible metal to metal connections which are corroding away.
On my 300TDi the system was very simple :- 50sq mm from the batt -VE terminal direct to the bellhousing bolt adj the starter. 25sq mm from the batt -VE terminal to the gearbox mounting and then onto one of the bulkhead earth points (M6 studs). From the bulkhead earth points (there are several) I then ran a separate earth (44/0.3mm I think) down each wing to behind the headlights and another through the chassis to the rear of the tub (the new Autosparks chassis harness already contains a link between O/S & N/S rear corners). At the end of each earth is a stud bolted to a suitable surface onto which each circuit terminates using a ring terminal. All circuits connect to one of these earth points (some are mine and others are existing points used by the factory, even behind the dash) and none is further away than the original earth (indeed many are closer). Of course if there are multiple earths (i.e. too many) at any one point then a second stud can easily be added and strapped across to the adjacent one.
I only upgraded my wiring recently due to the fact that I was replacing the chassis and it makes sense to fit new instead of what I first fitted 20-years ago and had proved totally reliable.
What do we do when we put our LR's together? We try to isolate the different metals as far as possible to avoid corrosion.
We make sure all surfaces are painted, use rubber / plastic / nylon gaskets where alloy bolts to steel, use nylon washers to insulate the steel washer from the alloy, use grease to act not only as an anti-seize lubricant but also as an additional isolating layer etc etc. Having done all this good work it is very likely that there will still be metal to metal contact at multiple locations and you could probably get away with (for example) relying on a self-tapper into the rear tub to provide an earth to the rear lights but it is not perfect and we have all seen the white powder corrosion that forms in time. How many queries are there on this and other forums where the first answer is to "check your earth" or alternatively "why is my handbrake cable smoking"?
Of course you could get past this by making sure that you clean all the paint off the mating surfaces before bolting the body together and making sure that the bolts make a good metal to metal contact but then you have deliberately gone and created what we try to avoid.
Likewise the chassis, we try to rust-proof the steel chassis with paint / underseal / zinc etc but then go out of our way to create a metal to metal contact in what is usually one of the areas most susceptible to road salt & muck.
The easiest solution is not to rely on the body or chassis to provide the earth and instead run separate earths to the various earth points around the vehicle (there aren't actually than many), easy to do and as long as you make the terminations secure then you will have a reliable set-up and the beauty is that if you ever do have a problem you only have to check the earth points, not go chasing possible metal to metal connections which are corroding away.
On my 300TDi the system was very simple :- 50sq mm from the batt -VE terminal direct to the bellhousing bolt adj the starter. 25sq mm from the batt -VE terminal to the gearbox mounting and then onto one of the bulkhead earth points (M6 studs). From the bulkhead earth points (there are several) I then ran a separate earth (44/0.3mm I think) down each wing to behind the headlights and another through the chassis to the rear of the tub (the new Autosparks chassis harness already contains a link between O/S & N/S rear corners). At the end of each earth is a stud bolted to a suitable surface onto which each circuit terminates using a ring terminal. All circuits connect to one of these earth points (some are mine and others are existing points used by the factory, even behind the dash) and none is further away than the original earth (indeed many are closer). Of course if there are multiple earths (i.e. too many) at any one point then a second stud can easily be added and strapped across to the adjacent one.
I only upgraded my wiring recently due to the fact that I was replacing the chassis and it makes sense to fit new instead of what I first fitted 20-years ago and had proved totally reliable.
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