I was getting my herd of cars ready for winter yesterday and remembered that my 914 had a very dull glow from the alt light, time to look see. The battery ground had some crud, as did the post, but want came to light under the sun was the 'Green Crud' in the bundle of wires that make up the ground, under the plastic covering. Any chance this is causing the dull glow of my alt light? Does this 'Green Crud' infection, fatal? Serious note: How long a ground wire do I need to buy? Is there a battery clamp that would allow me another hook up for my MSD? Same question for the hot side? Bob

If you can see the corrosion, it's time for a new cable. The corrosion causes a voltage drop on the system. I can contribute to poor charging and poor starting.

I once saw a guy that changed his Starter, Alternator & battery only to find out he had bad battery cables. All that money wasted before a $10 CABLE WAS REPLACED...

Elaborate. I read something similar to this recently. How long should we expect cables to last. Should they be checked/replaced every 5 yr's? Is this found predominately on the neg cable? Not necessary in arid climates? What is the preferred cable type? etc, etc ? TIA High jack over.

How long and how heavy a ground do I need? Bob

Battery cables should be inspected and replaced. A 5 year interval is a good start. Inspection includes visual corrosion and swelling or lumpyness of the insulation. This would indicate corrosion on the length of the cable. The corrosion becomes a "load" to with the voltage, pushing the current will be reduced trying to pass the load. Thus creating a voltage drop. 12V at the battery may be less than 8V at the starter. Voltage drop can only be measured under load. Or, take a voltage reading at the starter while you are cranking.

Size of cable should be as large as possible and no smaller than a #2 Copper wire.

Your local FLAPS will sell you a 4ga 18" ground cable for about ten bucks, which will work just fine.

At this length the difference between 2ga (about 250µΩ) and 4ga (about 400µΩ) is irrelevant (less than 40mV @ 200A cranking); the condition of the connections at either end is much more important.

Make sure the crimps on your cable are tight - with wire this size you should be able to pull on them with all your strength and not feel any movement at all in the wire. If you can rattle the wire around in the crimp, cut it off and throw it away.

Make sure that the brass ring on the body earth is clean and shiny (not brown), and don't put any sort of washer between the cable eyelet and the brass ring. Use a washer on top of the eyelet to help squash it down to get maximum contact surface.


However, the condition of the earth has nothing to do with the glow from your alternator light. Unless you have a short behind the instrument panel or somewhere on the blue wire that runs to the alternator field winding, the dim glow would suggest something wrong (most likely one of the smaller diodes failed) inside your alternator. You should not be feeding current to the field windings once the alternator is bootstrapped.

mikesmith, sounds like you work in aerospace as well.....
Worked in MV & loved the morning fog rolling over the mountains every day

The closest I get to aerospace is designing drone software for fun, sadly, but it's a great source of inspiration for "do it once, do it right or else".

Driving 280 in the afternoons, you could swear the sea is breaking over the hills. Still freaks me out sometimes after 15 years...

Just put a new ground cable in with my new battery. Got a 10" for the battery to chassis.

10 foot cable? Bob

10 foot? how far away from the battery do you need to ground it?

Sorry to hijack.... does anyone know where to get the ground lug that is attached to the body above the battery? PET shows no part number that I can find.

Also, can it just be drilled/ground out? I couldn't tell if it was welded in there.

While I'm at it, I might as well replace the one in the trunk too. Could I just use a bolt welded in?

Either Bob is being facetious, or he confused " (inches) with ' (feet).

Even so, 10' at 4awg is ~2.5mΩ, or 0.5V drop at 200A cranking. That's still better than your average corroded ground connection...

He used the excess to wrap around the battery, thus securing it and eliminating the need for excess tie downs.

BTW...
' = feet
" = inches <--

The ground posts were considered part of the chassis, so no separate part number. It's M8x1.25 thread and the originals were brazed in place. But welding an M8 bolt in it's place is standard repair. Just make sure to clean all the old brass off.