Lotus Elan

Battery Earth in boot

PostPost by: bitsobrits » Tue Aug 20, 2019 12:04 am

Having seen a few comments on the proper location for locating the battery ground in the post about diff mounting, I thought I'd comment:

I've owned a few Elans over 35 years, and all came with the trunk mounted battery grounded to one of the rearmost body mounting points at the bottom of the boot floor. So I'm pretty sure this is the way they left they factory.

It is also, IMHO, probably the worst possible place to ground any part of the electrical system. The rearmost holes in the chassis are "though" holes (no thread) so the ground between the chassis mounting bolt and the chassis is based on having a good bare metal connection between the bolt head and the chassis. Then the usually plated steel bolt passes through a threaded pot metal bobbin to which one attaches the earth cable with a nut. It all works until you actually start using the car and after a couple of years the bare metal connection is rusty from puddles and car washing and any oil dribbling from the engine or gearbox have further increased the electrical resistance at this joint. The bobbins also can corrode, if one is using a non stainless fastener, further adding to issues.

So on every one of my Elans I've fabbed a new ground cable to attached to one of the welded captive nuts (cleaned with a tap, then nickel or aluminum based antisieze) of the diff rubber mounts, using a stainless stud with a spacer to raise the cable to approximately even with the body panel (makes it easier to remove, if needed). Sometimes a bit of fiberglass removal is required to get clearance.

Then no more concerns, ever, about electrical grounding in the rear of the car. Similarly, I use the threaded body bolts behind the dash and into the front shock towers as proper grounding points in those parts of the car.

Here's a photo from my current project: (the spacer will be shortened to about body height after final install)
Cable terminal then clamps between the two nuts, with current carried by the stainless stud.
img_0087-2.jpg and

Elan S1 1963-Bourne bodied
Elan S3 1967 FHC pre airflow

Elan S1 1964
Elan S3 1966 FHC pre airflow
Elan S3 1967 FHC airflow
Elan S4 1969 FHC
Europa S2 1970
Esprit S2 1979
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PostPost by: MarkDa » Tue Aug 20, 2019 8:04 am

A very neat solution which I may adopt as I've had problems losing the ground but the boot bolt.
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PostPost by: wotsisname » Tue Aug 20, 2019 8:55 am

Lotus recognised this at some point in the +2 production and moved the battery earth to the strut brace behind the seats. The aerial was earthed to the diff mount on some +2. That looks nicely made
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PostPost by: Frogelan » Wed Aug 21, 2019 9:26 am


Thank you for your very informative post and photo. A very elegant solution indeed.

I'm not planning to put the battery in the boot but this can be recycled elsewhere in the car as earthing/grounding is a question that I had not yet found an answer to.

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PostPost by: alan.barker » Wed Aug 21, 2019 11:10 am

In a plus two that solution will be difficult with the Fuel Tank
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PostPost by: The Veg » Thu Aug 22, 2019 2:18 pm

alan.barker wrote:In a plus two that solution will be difficult with the Fuel Tank

Indeed. Luckily my original chassis earth seems to be good but definitely worth maintaining, or investigating alternatives that could employ a similar upgrade.
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PostPost by: MrBonus » Thu Aug 22, 2019 5:47 pm

The ground in my trunk failed too. This was discovered while rewiring. Thank you for this thread as it is quite informative.
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