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Hi,
What you have there is normal for factory.
The extra lug could have and most likely someone’s additional ground for an accessory.
While you are under there give the positive wire under the crankshaft pulley a good cleaning.
Any seal leaking goes on the sheathing.
If it rubs itself to ground, via the engine blocks underside it can be toasty.
The engine has its own ground because in essence the power train is sitting on three rubber mounts.
You should have two ground wires coming off the negative post.
One to the engine ground and another one to the left fender for a body grounding.
A ground is one-half of all circuits, plain and simple .
The current flow is out to all components and back to positive terminal through controllers.
Disconnect the negative battery terminal stops all sparks.
If you only undo a positive side of a component then the wire can still spark to ground.
Inspection of your grounds is very wise maintenance to keep what seemingly doesn’t move, working.
There will also be a flat braided fine sized wire running to the firewall to a valve cover stud.
This is for electronics to have a closer ground for the injectors, but sensors using very low signal voltages things happen.
The braiding disrupts the paths of higher frequencies, than can induce currents from what seems to be nowhere.
For instances with ignition system wiring and radio static.
This is a very passive in idea but made more robust in these years.
Borrowing from Michael Faraday’s Capacitors and Nicolas Tesla safety cage.
It’s much like what is called shielding inside signal cables today.
How effective those on the 240s were is anyone’s guess. Must be something to spend an extra coins and was a concerted effort from an area of R&D to tool it into production.
I have pondered the usefulness of putting ignition coils right on top of the spark plugs and have them subjected to enormous cycles of heat.
Have you seen prices on new car replacement coil packs from FCP Euro.
Tune up kits? I don’t know how they afford to stock them or sitting on anyone’s shelf.
Whoops, wait a minute, mark up(s) are there. Tennis is not the only game using rackets!
A Failure rate, you bet cha!
Scott Kilmer chases them all the time with his Elimination technique.
Phil
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