New to me 911 - Need alternator wiring help!

[LuvNH]

1979 911 SC, with a ‘78 engine.

Key to run - I get the red charge light (as proper). Start it, let it run for a few still have red light on. Rev it a bit, light goes out.

Car off - voltage across battery was 12.6. While running, see 11.7 on cig lighter voltmeter. With a load (lights & such) see 11.4. Regardless of RPM.

Verified the readings with a vm across the battery.

Thought I had an old alternator with ext VR, but after I removed it to take it to get it tested, I think I have one with an internal VR. Makes sense, bc I never saw any wires besides the alternator noise connections connected to the external VR (it is still installed).

Wires appear to be intact after I removed the alternator, but I found there is a ground strap laying on the tops of the cylinders.

The Bentley manual says there is a ground strap connected to the alternator, but where?

And is this could be the solution to my problem? Don’t understand, in the current condition, why the red light goes out though.

[proporsche]

it is kinda wrong ground strap..it should be 0.5mm brown wire going the the joined ground on your alt. and the 1st stud-nut you see on your engine case

Ivan

[LuvNH]

PO did the work or had it done. Dunno.

You can see in the first pic the strap is connected at the 3rd case bolt (from the back I guess). I don’t feel like moving it unless it’s a problem which I cannot see it being.

But you say it goes with the other brown wires? The neg post?

[PeteKz]

I always thought the original brown wire was kinda lame for the amount of current the alternator can put out. When I replaced my old alternator/external regulator with the 175 Amp WOSP unit, I also replaced the brown to the case with a strap like that.

[proporsche]

The strap is ok if it long enough,on the pic i do not see the lenght -if not it is a PITA to instal the Alt. back to its place..and yes it goes together with the other brown wire..but you can use any ground point on the alt.
Ivan

[LuvNH]

Originally Posted by proporsche

The strap is ok if it long enough,on the pic i do not see the lenght -if not it is a PITA to instal the lat back to its place..and yes it goes together with the other brown wire..but you can use any ground point on the alt.
Ivan

You can see the entire strap in the first pic. I think it’s long enough. I’ll give it a go today and report back.

[LuvNH]

Originally Posted by PeteKz

I always thought the original brown wire was kinda lame for the amount of current the alternator can put out. When I replaced my old alternator/external regulator with the 175 Amp WOSP unit, I also replaced the brown to the case with a strap like that.

Great to know. I debated swapping it back, but this helps.

[PeteKz]

If the strap gives you enough room to get the alternator in and out, then keep it.

[LuvNH]

Cleaned connections on the back of the alternator. Had one rubber boot and had to get another one (thanks to the forums here). Placed one on the red wires and the blue.

Installed everything and moved shims around to get proper tension. I have to double check belt movement per Bentley manual.

Voltage across the battery was 12.43, a little low but wanted to get this test done.

Started the car, red light illuminated. Voltmeter in cig lighter said 11.7v.

Let it run for a few minutes. Revved Eng and light went out. No change in voltmeter.

Got out and checked fan to ensure it wasn’t slipping. While I was out of the car, the engine suddenly idled lower. Voltmeter read 14.0!

Got back in car, and watched it for a minute, no change. Then I loaded it up with lights, and voltage read 13.7.

Then the voltage dropped and went back to 11.7. Regardless of engine speed. Idle went back to normal.

Red light was dark. Turned car off and restarted, no change.

After putting car away light does work with key in on.

No fuses blown.

I think all this points to the resistor that should be installed by the red light. I’ll see what’s there.

Any other ideas? Been pouring through the forums and see that the alternator and vr may be the culprits as well.

Thanks all.

[LuvNH]

I think I may have found my problem.

Pulled the gauge. See pics. I do not see a resistor anywhere. Am I missing it?
Guess I’ll have to add that. I have seen that mentioned many times. More reading!

Additionally, I found an unattached green wire in the bundle behind the oil temp. I have reviewed the elec diagrams from the manual and don’t see one besides the fuel gauge, which is present. Could it have been part of the harness that was made for the blank light at the top of the gauge? There is a piece of tape covering a port on the rear top of the gauge.

[mysocal911]

Originally Posted by LuvNH

I think I may have found my problem.

Pulled the gauge. See pics. I do not see a resistor anywhere. Am I missing it?
Guess I’ll have to add that. I have seen that mentioned many times. More reading!

Additionally, I found an unattached green wire in the bundle behind the oil temp. I have reviewed the elec diagrams from the manual and don’t see one besides the fuel gauge, which is present. Could it have been part of the harness that was made for the blank light at the top of the gauge? There is a piece of tape covering a port on the rear top of the gauge.

Some of the internally regulated alternators need a resistor (~ 100 ohms) in parallel with the alternator light to provide adequate startup field winding current.

[al lkosmal]

Here is the resistor info.......

[spoke]

Originally Posted by LuvNH

Let it run for a few minutes. Revved Eng and light went out. No change in voltmeter.

If the GEN light stays on when starting the engine you should blip the throttle immediately to get the alternator functioning. Not having the resistor you spoke of may help eliminate this startup issue.

My 914 does this when starting if I don't rev the engine. It doesn't hurt anything although as long as that light is on the alternator isn't functioning.

Got out and checked fan to ensure it wasn’t slipping. While I was out of the car, the engine suddenly idled lower. Voltmeter read 14.0!

Got back in car, and watched it for a minute, no change. Then I loaded it up with lights, and voltage read 13.7.

Then the voltage dropped and went back to 11.7. Regardless of engine speed. Idle went back to normal.

This is not the resistor issue. Sounds like you have an issue with the alternator/VR. Sounds more like the VR having issues.

One thing to check when the low voltage occurs is to measure the voltage on both sides of the GEN light. They should be equal with the GEN light out. If they are equal and around 11.7V, then it seems your VR is not up to the task.

Also have your battery checked. I had a low voltage issue with my '86 930. Battery voltage didn't get over 12V and car would barely start. Opted to change the battery and got 14V immediately.