What a bad earth looks like

[pete3000]

Did a spot of fault finding last weekend, after a failed start mid week. The instrument lights would come on glow plug etc, then went for crank and nothing. A vague click could be heard from the solenoid but nothing else. Along with this all the dash illumination went dim/off. So I put the batteries on charge and swapped to the car for the night.

Came to it a day later, same thing. Thought this isn't good, after all it flew through it's MOT in August.

12.75v across battery - 12.6v ign on and crank

12.62v at starter (engine earth) 5.5v ign on and crank

12.62v at starter (engine earth) 2.5v ign on and crank with lights on sidelights

moved earth from meter to battery and remeasured the starter terminal 12.72v (more like it) 12.5v with ign on.

So pinched a single black jump lead and jumpered the batt negative to an engine earth (lifting eye) and tried the starter, bingo!

This is what i found when I took the main batt-gearbox earth off, looks mechanically sound but it was dropping 7-10 volts. (35mm cable and m10 eye)

Remade it with a hydraulic crimp then filled with solder, much better now, and lights are brighter too

[Tanuki]

That's a classic example. And a classic fault-finding technique too. Congrats on finding "one easy fix" that solved a number of issues.

The bottom end of the battery-to-block/chassis earth lead is invariably exposed to all sorts of nasties [road-salt, wheel-spray, mud and water if you do much wading] and Sod's Law dictates that the least-visible connections are the ones that always want to fail!

[Nigelw]

Oh yes, one of the main reasons I have a strap from starter battery neg to the block, it worked grpm new going round the houses via the chassis but age and corrosion shown here adds up!!!

[mickeyw]

I had the same thing with a winch motor negative.

I couldn't see anything physically wrong with the connector or crimp, but chopping a couple of inches off the cable, and crimping on a lug made a world of difference.

[HoSS]

Always a good idea to solder these large lugs after crimping. Keeps the air out (corrosion) and improves the resistance.

[FridgeFreezer]

Surely this is a candidate for the technical archive?

HoSS - vaseline is a good alternative too, generally you can slather any connector in it to keep water out.

[GW8IZR]

On a new lug and new cable I'd crimp then use glue lined heatshrink, many advise against petroleum jelly or silicon grease but I have always done it unless a customer specifically says not to.

On an old cable that didn't come too clean I'd use a good flux and solder, horses for courses, I think there was a recent thread on this :-)

[western]

Surely this is a candidate for the technical archive?

Agreed & linked to our Tech Archive 'Electrical' section as Bad Earth fault finding,

[Boydie]

All of my earth and main battery terminals were the same, shoddy mass produced crimped connections.

My solution was to immerse the terminal ends in some old battery acid to remove all the crud and clean the oxidisation off the copper wires, I then rinsed them in clean water, used the cooks hair drier to completely dry them and just soldered them tinning the terminals to reduce future corrosion. Job done and great connections.

I also found that where the main earth from the starter motor bolts to the chassis the paint was preventing a good earth so I scraped away the paint to reveal bare clean metal. Once I had re-connected it I smeared the bolted terminal with silicon to reduce any future corrosion. New star washers that bite into both surfaces are, in my opinion, essential at these chassis connections.