Poor main earth connection

[ChrisC]

Chaps,

The answer to this eludes me...

Sometimes, I try to start the car and it *appears* that the battery is totally flat and I mean totally - not even the panel lights work. However if I undo the battery earth lead from the bulkhead and then reconnect it, the car starts and runs just like you would expect. Clearly I have a intermittent bad earth.

I have over time, removed the standard bolt and replaced it with a brass one, replaced the earth lead with a new one, cleaned the terminals I don't know how many times, tried brass washers, I have even sanded the bulkhead back to bare metal, bolted it all back together and liberally coated the connection with lithium grease. However I still don't seem to have permanently solved the issue and on occasion I will have to remove/replace the lead to get the old girl running.

Does anyone have any smart ideas, does high conductivity grease exist which might stop the connections corroding?

[MSM]

Chris

With the amount of time you have spent on the earth lead it is probably now fault free.

What about the other battery connection? Or it's connection to the main stud under the heater box? What about the connections on either end of the lead from the stud to the starter? There is also a flexible earth lead under the car on the exhaust side adjacent to the reaction plate - worth a look.

Good luck.

[abowie]

Chris

With the amount of time you have spent on the earth lead it is probably now fault free.

This was my feeling when reading the original post as well. I've seen some pretty shitty rusted frayed engine earth leads and they all seemed to work.

[cactusman]

It is also possible that the fault is within the solenoid. Mine was sometimes very sluggish....other times ok. New solenoid (mine is not part of the starter) and the problem was gone.

[Simonpfhc]

New battery time!

[ChrisC]

Thanks but no its won't be the solenoid, engine earth strap or the battery itself.

If I touch the battery earth strap too earth with a spanner I get a small spark - which implies its the connection on the bulkhead. Its almost as if the terminals are oxidising over preventing connectivity.

As I say, loosening the earth terminal on the bulkhead and then retightening it, means the car starts right away - even if before I do that, the battery appeared to be totally flat. I keep a battery conditioner on the battery so its always charged up.

It *is* a weird problem - hence the reach out to you guys as I am running out of ideas :)

[mgcjag]

Hi Chris you mention if you touch the earth cable to earth you get a spark.......is this with everything turned off?.......also are you running positive earth......dont ask me the technicals but there is cathodic corrosion....possible since you changed to a brass bolt for the body connection....(dissimilar metals)...i know no more than that so dont try to shoot me down ...im just throwing something into the discussion.....Steve
PS dont know about Lithium grease....but silicone grease or Vaseline for electrical connections....

[cactusman]

If you are certain it is corrosion at the main earth then dismantle the termination, put a shamqe proof lock washer under the tab so it sits between the tab and the body. Plenty of Vaseline and tighten up. The washer will cut into the tab and the body and make a good electrical connection while preventing any loosening and hopefully the Vaseline will deter corrosion. Excess can be wiped away once tight.

[ChrisC]

Ive just been reading up on conductive grease, I sense a test session coming up tomorrow to see which one conducts electricity the best. Vaseline was mentioned but that's petrol based, but I can play with lithium, silicon and copper grease - I will report back :)

[ChrisC]

Darn...
My bad battery earth cable problem has returned. I thought I had solved that but no. Same issues as before - loosen the earth lead on the bulkhead, clean the terminals, tighten the securing bolt up again and the car is fabulous again.

Conductive grease extended the period between needing to do this but it didnt 'solve' the problem.

I think might daisy chain battery-engine-earth so that in theory would double up the engine earth but I would at least have 2 earths :)

On a side note I have owned and loved my S1 Etype for 36 years but my bad back is making getting in and out the tiny door a bit painful. Maybe I need to rebuild a series 2 roadster and make my life easier :)

[Series1 Stu]

Is your car positive earth?

Regards

[Joes66]

This sounds like a poor connection between the chassis and the main earth to ignition and services to me
Or a poor live connection
You say the lights sometimes dont come on
This rules out the starter motor and the solenoid
Its probably a bad connection/faulty ignition switch or something like this
Check around the fuse box as well and the fuses
I am guessing it has the chassis to engine strap fitted so you should check that also
The strap from the battery to the chassis is not rocket science, it's a basic thing that from the sounds of it you have fully tested so I would look elsewhere
Joe

[44DHR]

Chris,
Sorry, just seen this post for the first time.
I run two Earth leads, in respect that the battery Earth lead bolts directly to the horizontal area of the engine block just behind the dipstick and an “open” flexible braid connects from there up to the body earth mount.
With reference the starting problem, this can happen in similar situations with an associated intermittent fault, where the battery appears fine, with all dash lights on, then these dim as the car fails to start as the ignition key is turned, giving the impression the battery - or battery connections - such as the Earth are at fault. Having then disconnected and reconnected the battery, sometimes when trying the ignition key again, the car starts !
My initial thoughts in this instance are twofold, depending on the Starter Motor and if the car has a Starter Button.
Firstly, sometimes the wire to the starter solenoid becomes loose - especially on replacement High Torque starter motors as they use a single small modern spade terminal as opposed to being a bolted connection. With a loose connection the starter will not work.
Secondly, and the most likely is the Ignition Switch itself. This takes a very high load and can become intermittent as the contacts burn out over time. On trying to start the car, all the dash lights are correctly fully illuminated when the ignition key is turned, but on pushing the Starter button, there will be a click as they will dim as the switch cannot transmit the high current to the starter button.
The best solution is to fit the Ignition Relay to overcome this problem and have trouble free starting.
Detailed in this post with my comment at #9 and my references :-
viewtopic.php?f=3&t=15658&p=128135#p128135
Stay Safe,
Cheers,
Dave

[ChrisC]

Thanks Dave - the ignition switch having high resistance had not occurred to me and is worth looking at as it is an after market item and it may indeed be a contributory factor. A relay would get round that problem at least.

But the bit that niggles me is why cleaning the earth strap to bulkhead connection immediately solves the problem and the high torque starter really whizzes the engine round. The issue stays resolved for months then occurs again no no good reason. So I just undo the earth strap - clean - tighten and then drive as normal. its just annoying :)

[Heuer]

Daub the terminals and screw with petroleum (KY) jelly to prevent oxidisation.

[Series1 Stu]

Hi

We use ZX13 graphite loaded grease for all exposed earth connections in marine and aeronautical applications. It isn't cheap but it is about the best protection you can get. Obviously, £40 for a 500 gram tin is a lot and you'll probably not get through half of it in a lifetime but, like red rubber grease, its a valuable ally to have in the garage. Maybe buy a tin and share it with friends.

It meets lots of military and aviation standards and has a Nato Stock Number so you should be able to find a supplier pretty much anywhere in the World.

Regards