Trunk (boot) ground location & wiring

[stugilmour]

My car appears to have a few modifications over the years, including a cut off flat grounding strap artifact under one of the diff mounts and a heavy ground wire to the front of the car. Manual seems to indicate rear body mounting bolt.

Where should the battery be grounded?

If the body mounting bolt is the correct spot, do I need a flat ground strap or would a round one fit, and what length should I purchase?

Is it sufficient to have the ground strap securely under the head of the selected frame bolt, or do I have to scrape paint off my lovely new frame and somehow run the wire separately outside the fibreglass?

I am working with just the frame at this point as the body is out for paint, so any help appreciated.

thx

[gerrym]

Stuart, as you have stated, the earthing point for the battery (and therefore the entire vehicle electrics) is via one of the rear body to chassis mounting screws.

The major shortcoming here is that the interface between the chassis and mounting screw (3/8" UNC) is exposed to all the road elements, leading to corrosion and therefore high resistance.

My modification consists of an additional screw WELDED to the chassis, centrally located between the 2 rear chassis to body screws, facing vertically upwards. The top of the approx 2" long screw is ground to a tapered end, there is an additional hole in the body to match.

When lowering the body onto the chassis, this tapered end acts as a "stab-in" and guides the body into the correct alignment with the body. The essential thing is that the welded connection now ensures a low resistance electrical joint, and one which when painted is immune to corrosion. The threaded joint making the electrical connection to the chassis is now in the relative dry environment of the boot, and can be protected using die-electric grease or even vaseline. Overall, the chassis can now be expected to provide a reliable earthing structure.

Regards

Gerry

chassis earth.xls

(254 KiB) Downloaded 475 times

[mikealdren]

Stu,
As Gerry says, the standard Elan earthing isn't great. Another recommended mod is to run an earth up to the bolts that secure the body to the rear chassis uprights, these are threaded into the chassis so give a better earth and they are less prone to corrosion than the lower mounts in the boot floor.

Mike

[stugilmour]

Thanks guys. As do not have welding equipment easily available, will run to the rear chassis upright. IIRC I should be able to run the ground cable pretty easily beside the fuel tank without any holes in the body.