What engine grounding should my 1968 911 have?

[911scfanatic]

There's a thin, long pathetic looking black wire from the breather cover to the rear shock cross member. Clearly not factory. Is there supposed to be a more robust ground here? When I had the shroud off, there was no ground from the alternator to the nearby outer perimeter case bolt like there was on my '72 and '83. Proper ground info (w/ pics if possible) would be greatly appreciated. Also any p/n for ground wires would be helpful. TIA.

[Fritter]

I was wondering the same thing, no ground wire from fan to engine case on my '68 either. But who knows what changed over the last 42 years.

[911scfanatic]

Mike, saw your question re: sensor wire routing. I'll look on my '68 this w/e. If I don't get back to you in a day or two, please send me a PM reminder.

[Fritter]

Thank you!!

[edmayo]

Hi Fritter, I think there should be a ground wire from the back of your alternator over to the main grounding post on the left side of the engine compartment.

[Fritter]

Ed, yes, a brown wire from the post on the alternator, through the loom and to the post on the left wall, yep I have that. Just wasn't sure if one was needed from alternator to case iin the fan shroud. Seems the answer is no. Thanks!

[304065]

Mike,

The later cars have a copper ground strap from one of the D- posts on the back of the alternator to the case parting line bolts.

Why this is so recalls an oft-overlooked area of electrical engineering-- the conductor used for GROUND has to handle as much current as the conductor used for POWER.

Now, in the little 35A alternator, the 12 gauge or so brown wire in the engine harness is probably enough to handle the ground. It's only in the later 55A and much later (my Carrera used a 90 amp) that you really need the ground. Also, the wire harness acts as a heat sink, believe it or not.

That said, nobody can see it behind there, so you might add one "while you are in there."

Best,

John

[911scfanatic]

So what's the wimpy black wire on the breather cover? A PO has clearly installed it, but I don't know if it was a half-hearted attempt to replace a more robust factory wire that was previously there...

[Fritter]

If the black wire is going from a breather cover bolt to the alternator area, I bet someone added it for a ground.

I have more ????? after analyzing my rear wiring more today.....I have a black wire with a thick outer skin that never went anywhere, and I also have a solid green wire. These are factory, they go up into the hole into the tunnel with the rest of the wires. They are not on my wiring diagram I got off Pelican. My car was originally a sporto, so I think they may be related to that.

Calling Ed Mayo, I think you will know the answer to this one!!!!!

[304065]

If the black wire is going from a breather cover bolt to the alternator area, I bet someone added it for a ground.

I have more ????? after analyzing my rear wiring more today.....I have a black wire with a thick outer skin that never went anywhere, and I also have a solid green wire. These are factory, they go up into the hole into the tunnel with the rest of the wires. They are not on my wiring diagram I got off Pelican. My car was originally a sporto, so I think they may be related to that.

Calling Ed Mayo, I think you will know the answer to this one!!!!!

Mike, the green wire is the Sporto wire, I think it's for the microswitch on the gear lever. (To be confirmed by Ed, but even my '70T shell had that wire that's not on the diagrams)

Black with a thick black skin is definitely the factory, particularly if it's two layers of black PVC. Can you describe what goes in and out of your electrical console? Usually there is a fat black from the starter positive terminal that goes to the console, then a red wire with white stripe back around the crossmember to the hole in the shroud for B+. If somebody has done it like the later cars and run a wire directly from the B+ to the starter terminal, that could account for the "mystery" wire.