Is earth to chassis essential?

[Disty]

I have replaced my chassis, and the only earths I have are:

1. Battery -ve to transfer case.
   
2. Transfer case to bulkhead
   

Now I have an intermittent error where it sometimes won't start- after this all dash lights dim to practically nothing, and nothing gets power.

Is this an earth problem?

I don't see why it would be solved by grounding the chassis- nothing goes through my chassis. Am I being stupid?

I have attached a temporary cable from bulkhead to alternator and this doesn't seem to help. There is also no earth from the engine block to chassis/transfer case (does this not travel through the bell housing?)

[tacr2man]

You should have earth from body to chassis and from chassis to engine , the battery -ve usually goes from battery to body and on to chassis . Make sure a contact points are free of corrosion .

[oakesy]

Your earthing trying to find grounding via alternative source.So this might be interfering other power usage. Also the gearbox bellhousing and engine might not be made of the same material. intermittent error with your lights dimming could well be the battery being poor or not recharging correctly for reuse.

[Disty]

But if it is connected directly to the battery -ve on the back of the transfer case, isn't this even better? Why does it need to touch chassis at all?

I know I only have those earth's because I didn't put any others back on when I rebuilt.. Was running fine yesterday..

[oakesy]

Not being a serious electrician and feel free anyone to mock and slap the back of my head like an foolish child Pending on the condition of the bulkhead and fittings to the chassis. Also the engine and gearbox is only connected by the mountings to the chassis are weak points. Where a direct earthing strap cancel out any form of resistance level.

[Disty]

Ok just checked resistance between engine and -ve battery terminal - none!

Interestingly every time I try to start the car or indicate, the relays make a very unusual sound- has anybody come across this before?

[jbs]

My earth's are as follows: Battery negative terminal to the chassis, battery negative terminal to the back of the gear box, Chassis to block by the engine mounts(200tdi),then block to the rear of the starter motor

I will be adding more as I will be uprating my lights as per the other threads on here somewhere and it will need good solid earth's for that

[nickwilliams]

Ok just checked resistance between engine and -ve battery terminal - none!

Interestingly every time I try to start the car or indicate, the relays make a very unusual sound- has anybody come across this before?

The resistance of the battery/chassis/engine earth path should be very low indeed, such that you can't make a meaningful measurement of it with any normal kind of meter, so your resistance measurement probably isn't telling you anything useful. If you want to make a useful measurement, try measuring the voltage drop between the parts under high current conditions (e.g. when cranking the engine or with all the lights turned on). Anything more than half a volt is a good indicator of a poor earth connection.

Try using a good quality jump lead to go from the battery to the chassis or from the chassis to the engine and see if that helps - if it does it will tell you which path is causing you problems.

The relays may well make odd noises if any of the earth paths are high resistance.

Nick.

[western]

my '89 110 has

1.earth from batt neg terminal to main gearbox/transferbox joint bolt

2.earth from engine block/PAS bracket rear facing bolt to chassis part of left engine mount, I recently replaced this with a much thicker earth cable from halfords.

starter is earthed to engine by it's fixing bolts & to cahhsis via the earth lead described at 2 & via the engine gearbox casings to battery neg terminal.

[FridgeFreezer]

There's a lot of things (eg gaskets, joints, etc.) between the transfer case and the starter motor - mine earths battery -ve to starter bolt, battery -ve to chassis, and separate earth returns for everything to a busbar in the battery box, but then I'm picky like that.

Given that the only electrical bit on the transfer box is the difflock light switch, and that's not even ground-return, I'd move the earth to where it's needed (starter or at least engine block/bellhousing). Engine mounts are rubber and hence not going to conduct much to the chassis except through things like the throttle cable or heater control cables, and they're not really designed to run the starter motor.

The same applies to the bodywork earths - LR bodywork is a big and often loose assemblage of painted dissimilar metals plus random fasteners and assorted corrosion, so the path of the electrons back to the battery through the body is by no means smooth or guaranteed. Earthing the chassis gives more chances for success, but running ground return wires from the main earthing points to the battery makes things a much more reliable bet.

[nickwilliams]

running ground return wires from the main earthing points to the battery makes things a much more reliable bet.

In theory, at least, it should also help to reduce the corrosion which you rightly identify as a cause of problems.

Nick.

[TSD]

... so the path of the electrons back to the battery through the body is by no means smooth or guaranteed.

err, the electrons flow the other way Fridge(*)

Linky

(*) Except if you have +ve earth, which I know you don't

[V8 Freak]

Nah.. Fridge is south of Watford and thus falls into the Southern England electron pool..

They are a mixed and roudy bunch of electrons, but generally do what he says!!

Neil

(Coat, Hat, Door....)

[ThreeSheds]

It does sound very much like an earth problem - but could also be the battery connectors. It is possible to have a low-resistance between either cable and their respective battery posts, and yet still get very poor conductivity once the starter is turned - imagine a piece of five amp fuse wire making the connection - zero resistance until you hit it with the starter. I have seen battery contacts that will happily power the headlights, but fizz and pop when asked to take starter motor drain.

not going to conduct much to the chassis except through things like the throttle cable or heater control cables, and they're not really designed to run the starter motor.

FF makes an important point here - you may have sufficient earths now (although I would want more) but if one of them corrodes then high currents may be forced to try and make a path through other conductors - which may include any directly-wired accessories with obvious results. In the world of two-way radios it is common to have the unit wired (power and earth) directly to the battery - in these cases there is a fuse on both leads to protect the cabling from just this sort of potential problem. IMHO you (or anyone) should add earth straps anywhere that important heavy-drain equipment is located (again as FF suggested) - it's more a case of 'can I make it better?' than 'can I get away without it?'...

While I am slowly adding more earths to my RRC, the current setup is (I think) ok:

Separate fused earth leads to battery for Megajolt, electric fans, driving lights and switched triple accessory socket.

Strap from battery to off-side body earth point.

Strap from above to bell housing (starter bolt)

Strap from back of cylinder head (other side) to bonnet

Strap from back of cylinder head to near-side body earth point.

I think there may be one other, but it's dark out there...

Hope this helps,

Roger

[Disty]

Roger! You were spot on! Turns out it was the battery connection! I feel a bit stupid now. emery paper and some contact grease later and all was working smoothly.

Needless to say, I'll be going to buy some earth straps this week to bolster the earthing situation. I still might leave the chassis out of it as I don't fancy stripping the schutz.

[cypermethrin]

So would I be right in thinking in order to ensure the best possible earth connection for a starter motor it would be to connect it directly to the battery negative terminal with some heavy duty braided - rather than relying upon earthing it to the chassis ?

If so can some bight spark (see what I did there !) advise on the length of braiding required from starter motor to battery box in a std 90 300TDi - I clearly need to order one.

[Cartman]

Cyper,

2' 6" should be more than enough. Go for 16mm CSA if poss. 10mm CSA as a minimum.

All my past and present LR fleet have had additional earth bonding fitted to the chassis. As Fridge et al point out the mish mash of mixed metals never lends itself to being a quality conductor - and then corrosion comes into the mix

My simple system in addition to the std set-up is a 10mm CSA braided bond to the chassis. I use a brass screw drilled and tapped thro' then coated in coppaslip/vas. Then a smaller braid to a central point at the rear of the chassis for the lighting array, and the same for the front (it's amazing how much brighter the lights can be after that!).

[UdderlyOffroad]

I have to disagree, the voltage drop accross a long length of braided earth strap will be far more than two short lengths (battery to chassis, chassis to starter motor), even taking into account doubling the number of connections needed.

Both my donor-discovery and my project 110 came with a strap from the starter motor to the chassis, and a strap from the chassis to the battery. For once I agree with LR's way of wiring and I would encourage you to do the same, even if it does mean cleaning off some of your schutz. You can protect the bare surfaces from corrosion through generous application of copperslip.

[gazelle]

LR bodywork is a big and often loose assemblage of painted dissimilar metals plus random fasteners and assorted corrosion

Best description of a Defender I have ever heard.

[Pendant mode on]

Would just add a "badly" in front of "painted" to make it more accurate!

[Pedant mode off]

[LR90]

'random fasteners' aka zip ties and gaffer tape

[FridgeFreezer]

I have to disagree, the voltage drop accross a long length of braided earth strap will be far more than two short lengths (battery to chassis, chassis to starter motor), even taking into account doubling the number of connections needed.

Is that based on science or opinion? I wouldn't expect two extra joints and a length of slightly crusty steel to perform better than a nice length of copper, plus it has two extra chances to fail.