Alternator

[porscheboy1]

For a 1978 911SC could someone post a picture showing how the alternator is grounded to the engine crankcase?

Thanks.

Once, if I remember well, I had a 1957 Speedster. We spent 13 years together.

[tirwin]

I have an '83 but maybe this will help. I have two grounds. One is in the wire harness that passes through the rubber grommet in the engine cover. The other is a short wire that connects directly to a nearby engine case stud back behind the alternator.

[Jdub]

See two examples here: What's the Best Way to Clean.

The first pic shows a braided ground in need of a good cleaning (corroded). The second shows what I have in my 1978 - a brown wire that is connected to the engine case via a nut (EDIT: Note also twin thin brown wires from harness as Tirwin has noted above). Remember, this is the first step in the ground, as the transmission-to-chassis braided strap finishes the full grounding of engine to chassis.

[porscheboy1]

Thanks guys. When re-assembling the engine after I re-built it I don't recall putting back the ground strap from the alternator to the engine. The engine runs great but it is running on the battery only. There is no increase in battery voltage with the engine running. Also the alternator light in the instrument cluster does not light with the ignition on and the engine not running. It never lights. I removed the instrument from the dash and pulled the light and tested it and it is good. Also the oil pressure light in the same instrument works. I am thinking that if the alternator is not grounded I do not have a complete circut and hence no charging. Is this right? The ground strap from the transmission to the car's body is in place. I guess I will have to bite the bullet and pull the alternator back and look at the wiring. Is there something simpler to check first? This car has the external voltage regulator.

Regards,

John

3.0 engine
PMO's
Web Cams, solex grind
J&E 9.5 to 1 pistons
SSI hex
Dansk sport muffler

[wwest]

I find it hard to believe that the alternator case itself isn't providing a good enough ground and the wire is just insurance. Seems more likely that the wire to initially magnetize the rotor, the bulb wire, is open or the internal VR is TU.

[timmy2]

External VR ground wire is grounded at alternator along with all other devices. Without the ground strap in place it may not be seeing ground. Easy test is meter the brown wire in the remote VR plug for continuity to ground behind the fuse panel at one of the main body ground locations.

[wwest]

The external VR can/may be in place but not being used....

[timmy2]

WWest:Since the OP said it was in use...I offered a way to test his grounding of the alternator body.
Even if it wasn't being used, if the wires remain it is still a path to ground.

For the OP
Here is a photo of my '78 alt hooked up correctly. The brown wire at the back is the engine ground wire.

[porscheboy1]

timmy2. Per your suggestion I metered the brown wire at the remote VR. I hooked my ohm meter between the brown wire and car chassis ground and got a reading. Does this mean that the alternator is properly grounded? What would be the next step in finding out why the alternator is not charging the battery and the light in the instrument is not coming on when the ignition switch is turned on ? BTW I am using the engine wiring harness that you built for me. Beautiful wok.

[timmy2]

Sounds like you have a valid ground to the ALT.
I would suspect the VR is faulty as the next suspect. With the 3 prong plug at the VR unplugged and ignition on, do you see 12v on the blue wire to ground?
Also, is the suppression device still being used? It is before the VR with a small wire set plugging into the VR. It could be bad, so just bypass it and plug directly into the VR.
Is your VR the original one in a tin can, or the newer style electronic one?
I replied to your email with my phone number if you want to call me.

[porscheboy1]

Dennis, I get 12 volts on the blue wire to ground. The suppressor was still there. I got rid of it and plugged directly into the VR. Nothing changed. The VR is the original one in the tin can. I have ordered a new VR. The picture of the one that I ordered shows an identical tin can. It will arrive after Easter and I will proceed.

Cheers!

[timmy2]

Picture of what you ordered may not be what you receive.
Probably the electronic replacement. (Hopefully in my opinion)
Enjoy the Easter egg hunt!