Bad chassis earth?

Golly - this has been really helpful. Yes, when I said I was looking for zero/some voltage between battery and chassis (etc) I was assuming the ignition was on so there was a voltage to measure. Should have been clearer.
I'm at work (and very busy) today and tomorrow, but next week I am going to tackle it. The posts above cover exactly the info I was looking for. Will post more when I get a minute, but I really appreciate the time and effort people have made in replying.

BlackDogZulu said:

I have heard this before. Makes perfect sense. As soon as the driveway isn't under water, I'm on it.


This is a new one for me. I'll have a look into that too. The headlights are pretty ineffective, much worse than I remember on my n/a 90.

Thanks both.

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http://www.paddockspares.com/boomslang-performance-headlight-loom.html

Or you can make your own, it depends where your skills are ...

https://www.landyzone.co.uk/land-ro...ps-quite-a-difference-in-candle-power.319129/

https://www.landyzone.co.uk/land-rover/headlight-wiring-upgrade.72348/

Thanks Dippypud. Looking into it.

Ok, quick update: the rain has stopped and the ground is drying out. The battery earth strap goes to a point on the chassis where is it held by a P clip, and then goes on to a bolt on the gearbox. The battery and gearbox connections seem tight and uncorroded. However, the cable is slightly loose in the P clip. It’s all covered in Waxoyl and needs cleaning up, but it looks as though the insulation has been stripped off for about an inch, and the P clip is supposed to earth it. If this is how it is designed, then I think I may have found the fault. I can waggle the cable in the P clip, not much, but there is movement and it certainly isn’t tight like a battery terminal. This matches the symptoms, right? Starter (direct earth from block to battery) is very strong, but headlights (earthed through bodywork & chassis) are rubbish. I’m going to take the cable off, clean up the connections and make the P clip tight around the cable core (assuming someone here confirms I have guessed correctly). If that sorts the problem out, I have my eye on a couple of bits from VWP that will do the trick.

Am I on the right track, guys? Funnily enough, since I had a good look at it all last week, checking things were tight AND NOT ACTUALLY DOING ANYTHING the temp gauge has remained firmly in the lower half. However, the headlights are still dreadful, so I’ll assume the issue is intermittent and fix it anyway. I know this is probably incredibly simple stuff to some people here, but I’m learning all the time. Thanks all.

Could easily be the issue. If the cable is loose in the clip there may be a build up of corrosion inside the clip which increases resistance as well as a poor connection so it might be worth trimming it back if possible.

As above - sounds like a good suspect to me.

Your headlights may benefit from an additional earth cable 'tween the battery and the star point(s) to which they are earthed... follow the black wire back from the bulb connector and you should find the (star) earth point within about 300 - 400 mm (ish) - or just do the boomslang mod and be done with it

I think you will find that the P clip isn't actually a P clip. It is actually a tabbed connector that looks a bit like one and is crimped on to the wire. They do come loose from the actual cable, mine did and I just couldn't get it to reliably tighten up so I ended up cutting the wire at both sides and fitted two standard ring terminals and bolted both to the same place. If you have been wiggling wires you have probably (and temporarily) created a better connection which has cured your gauge fault. Lighting is probably another issue, just get them sorted one at a time.

I'd leave the original setup alone and simply put a nice thick cable between the engine/box and chassis. It'll be better than the standard 'P' clip setup. I have this and also separate earths onto my inner wings from the chassis- you never know how much corrosion has built up between the wing fittings. Nice bright head lights here and a first time starter!

Starting has never been a problem, but the lights are terrible! Since I found the loose connection, I have checked the continuity between battery -ve and a screw on the dash. It started at around 0.2 ohm, but then I wiggled the earth cable and it went up to 150 ohm. Volt drop between the two points was about 150 mV to start with, and 400 mV after fiddling. Looks like the P clip (correctly called a flag on the parts list) is the culprit. (Don’t take those numbers too seriously, as they go up and down like a yo-yo, even as you watch them).

I’m going to remove the cable as soon as the weather and the wife’s job list allow (I have a few days off work), clean up and remake the flag connection, with a hammer if necessary. My guess is that this will cure it temporarily, and if there is a big improvement I will fit new earth cables - battery to chassis, chassis to tbox, block to chassis, bulkhead to chassis, and run the earth leads for the lights back to the bulkhead earth point.

I also have a bathroom to paint and two tonne of logs to cut and split, so the poor old LR is taking third place at the moment. Thanks for all the info.

BlackDogZulu said:

Starting has never been a problem, but the lights are terrible! Since I found the loose connection, I have checked the continuity between battery -ve and a screw on the dash. It started at around 0.2 ohm, but then I wiggled the earth cable and it went up to 150 ohm. Volt drop between the two points was about 150 mV to start with, and 400 mV after fiddling. Looks like the P clip (correctly called a flag on the parts list) is the culprit. (Don’t take those numbers too seriously, as they go up and down like a yo-yo, even as you watch them).

I’m going to remove the cable as soon as the weather and the wife’s job list allow (I have a few days off work), clean up and remake the flag connection, with a hammer if necessary. My guess is that this will cure it temporarily, and if there is a big improvement I will fit new earth cables - battery to chassis, chassis to tbox, block to chassis, bulkhead to chassis, and run the earth leads for the lights back to the bulkhead earth point.

I also have a bathroom to paint and two tonne of logs to cut and split, so the poor old LR is taking third place at the moment. Thanks for all the info.

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Tried the hammer technique myself but not very successful as the flag terminal doesn't go all the way around the cable and the strands in the cable itself also start to splay out

Kwakerman said:

Tried the hammer technique myself but not very successful as the flag terminal doesn't go all the way around the cable and the strands in the cable itself also start to splay out

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Yes, I can see how it wouldn’t be too successful. It’s just an idea to confirm beyond doubt that I have found the problem, and to keep the truck driveable until I can order some new earth cables in.

As above. I dont know Defs so well, but other 300tdi vehicles had many earth problems. Sometimes leading to ad hoc earthing through handbrake cables and similar. With hilarious results. Well...maybe not so hilarious - flames, and so on.
I put extra in earths as a matter of course, with new fittings and cable whenever I get a 300, now.

Right, a solution of sorts. I am really pushed for time at the moment, so as a quick and temporary solution I have bought an 18" earth braid from Halfords and fitted it between the chassis point for the earth cable flag (duly cleaned up and copperslipped) and the battery -ve. This is just to bypass the loose connection between the proper earth cable and the flag/chassis point. It only just fits, but it will do for the time being. Resistance between battery -ve and bulkhead as measured last time is now about 3 milliohms, and with ignition on there is a voltage drop of about 30 mV, rising to about 90 mV with the lights on. Not perfect, but a whole lot better. A quick test of the headlights after dark to confirm. Fingers crossed. Will report results.

Longer term, plans for a boomslang loom for the lights (and some Nightbreakers) and a set of custom earth straps from VWP to link block, bulkhead, gbox, tbox, chassis and battery.

Sounds good. 3 milliohms could just be the resistance of your meter leads.

I was quite pleased. With the meter set to milliohms, just touching the probes together gives a reading of 0.2 mohm, so I thought that wasn't too bad.

Headlights significantly improved - by 50% as a rough estimate. Still yellowy rather than the white of modern headlights, but much better for my early/late commutes through unlit lanes.

BlackDogZulu said:

I was quite pleased. With the meter set to milliohms, just touching the probes together gives a reading of 0.2 mohm, so I thought that wasn't too bad.

Headlights significantly improved - by 50% as a rough estimate. Still yellowy rather than the white of modern headlights, but much better for my early/late commutes through unlit lanes.

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What sort of meter are you using? Most standard DMMs only have a resolution of 0.1ohms (100 milliohms). Unless you have something special I would suspect that to 0.2 is actually ohms rather than milliohms as that would seem reasonable for a standard meter. On some you can touch the probes and then zero the reading to improve accuracy, either way a good result as things are working better

It's a Gunson Pocketmeter, nothing special. My mistake of course - it's reading in ohms, not milliohms. It's got scales labelled 200 ohm to 20 Mohm (I think) and I am reading on the lowest. I think I got mixed up with millivolts. My previous understanding of resistance was just continuity/no continuity.

BlackDogZulu said:

It's a Gunson Pocketmeter, nothing special. My mistake of course - it's reading in ohms, not milliohms. It's got scales labelled 200 ohm to 20 Mohm (I think) and I am reading on the lowest. I think I got mixed up with millivolts. My previous understanding of resistance was just continuity/no continuity.

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In your case the 200 ohm range is the correct one to use, ideally the lowest range the meter has is the best when carrying out continuity checks. Just remember the figure you get when you touch the probes and subtract that from you actual reading. In your case if a cable measured 0.5 ohms on the DMM then the 'true' reading would be 0.3 (after you subtract the 0.2ohms for the leads). Good luck with getting it sorted, always feels good when you fix one of the more challenging issues.

All seems to be well so far. Lights brighter and wipers slightly livelier. I’m happy the truck as a whole is working well and fit for Christmas visitation duties. Medium term plan is now to buy/make and fit a boomslang loom or equivalent, and to beef up the earths across the vehicle. I’m not sure about the location of the bulkhead earth. A search on the web suggests a location close to the servo, but all I have there is small nut with a couple of wires disappearing into the loom (others seem to have masses of wires, but perhaps that’s a Td5 thing; mine is a 300Tdi). Is this my bulkhead earth?



Many thanks to everyone who has assisted (so far). What a helpful bunch.

BlackDogZulu said:

Is this my bulkhead earth?

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Yes I believe so.