How to check which alternator is on 911 SC

sanandreas · 03-22-2019, 06:24 PM

Hi There.

have a 78 911 SC. The alternator red light turns on when car is off. I have done some testing and have narrowed the problem due to the alternator. (regulator is external).

My question is how I can determine which brand / model of alternator I have with out pulling the fan and alternator out. I want to but a repair kit or a replacement that matches.

car is in australia. I want to buy the part in USA where the car started its life.

Was thinking a remote inspection camera but not sure where to push it in or what to look for.
Any help would be welcome.

2aircooled · 03-22-2019, 07:55 PM

G'day Mate,

Alternator red light on with car off according to Bentley manual is either faulty alternator or faulty wiring.

Removal of alternator is not a difficult job to DIY, just take your time, label the electrical wires, take photos, and most importantly disconnect the battery first and foremost...
You can read the replacement procedure at:
https://www.pelicanparts.com/techarticles/101_Projects_Porsche_911/20-Alternator_Replacement/20-Alternator_Replacement.htm

After reading that page, you can also do a pelicanparts forum search for (heaps) more info..

The alternator on my 81 911SC also failed a few year ago, and I ordered a replacement unit from the UK, but actually realised that I could have just removed my existing alternator and get it repaired locally (took only 2 days).. I would have saved on shipping and time if I did that first...

The alternator on our cars are very simple and straightforward to repair... You should be able to to find an alternator repair shop that has parts and can fix older units in Australia. The shop will be able to test if your alternator is truly faulty or not, as the red light on could also be faulty wiring, which is what happened to me just last month..

____________
Jeff

1981 911 SC Targa RHD (VW support vehicle)
1971 VW 1302 RHD (Porsche support vehicle)

sanandreas · 03-25-2019, 03:56 PM

OK to answer questions I managed to remove the alternator.

1. I didnt do any work on the car. I bought it like this.
2. I dont know how the wires go . this is what I have in pic.
3. I cant see a diode pack. this is a marchall alternator. Any idea where I look?

sanandreas · 03-25-2019, 04:00 PM

some pics

sanandreas · 03-26-2019, 11:56 AM

OsoMoore · OsoMoore's Garage

When I had concerns about my alternator (79 SC, built into fan) I took it out and took it to a local small engine/alternator/motor shop. The guy there cleaned it and lubricated it and put in new brushes. It cost me $20.

Trackrash · Trackrash's Garage

Sounds like a diode in the alternator is bad. There are shops that specialize in alternator repairs, they should be able to diagnose and possibly repair yours.

You can't rule out the regulator, however. What regulator is in the car?

GenX Porsche · GenX Porsche's Garage

First of all I would buy one of these,INNOVA 3721 Battery and Charging System Monitor https://www.amazon.com/dp/B000EVWDU0/ref=cm_sw_r_cp_api_i_t65MCbQ8VRG1S , so you can keep a close eye one what’s going on in your charging system because you could be cooking your battery if volts are too high. I had an issue with my voltage regulator, common problem, and decided to go rebuilt alternator as the cost was a small difference for the piece of mind.

The diy isn’t bad however separating the fan from the housing can be intimidating. I had success with this technique, http://forums.pelicanparts.com/porsche-911-technical-forum/60368-fan-hsng-alternator-removal.html.

theiceman · 03-27-2019, 08:29 AM

yup that is the original marchal from 1978, sorry to be late to the party but I could have told you that as I have the same car. With the same original Alternator.

You can get it diagnosed and fixed, or upgrade to a more modern alternator with a built in regulator ( no need for the external anymore ) . There is a TSB for this as Porsche did this also. You will have to modify your air guide a little and do some small rewiring but no big deal.

I don't have the TSB anymore but I'm sure someone on here will..

sanandreas · 03-28-2019, 03:31 PM

I want to keep it original.
Does this unit have a diode pack? I removed the brushes module off but it couldnt see any diodes on this. Where else would it be on the unit?

30westrob · 30westrob's Garage

To get to the diodes you have to disassemble the alternator. If you look into the back you can see some of the power diodes. Your alternator has 6 power diodes and 3 for field excitement.
The above recommendations to seak out a shop that specializes in alternator repair are well advised
Rob

911SauCy · 911SauCy's Garage

Not that I know a lot, but that does not appear to be the proper alternator.

I recently did a motor install, had the fan and alternator out, there were only 3 electrical connection studs coming out of my original, and correct '78 SC alternator...

sanandreas · 12:52 PM

911SauCy if you have a look you will see theiceman also has the same alternator as me. I have the original external regulator as well. And from the documentation and pics I have seen of others, there is definitely more than 3 stud points on it.

Perhaps your alternator is not the correct one, or there might have been several different versions used. It could be you had the regulator upgrade where it is integrated into the alternator and not external.

boyt911sc · boyt911sc's Garage

Quote:

Originally Posted by sanandreas

911SauCy if you have a look you will see theiceman also has the same alternator as me. I have the original external regulator as well. AQnd from the documentation and pics I have seen of others, there is definitely more than 3 wires attached to it.

Perhaps your alternator is not the correct one, or there might have been several different versions used. It could be you had the regulator upgrade where it is integrated into the alternator and not external.

Sanandreas,

You are indeed correct. I too have a ‘78 SC. It has four (4) wires to the alternator with external voltage regulator. Then I converted the alternator to integrated VR (refer to technical bulletin regarding the conversion). Now, my ‘78 SC’s alternator has the three (3) wires similar to those late SC’s.

Tony

sanandreas · 03-30-2019, 01:25 AM

So has anyone with the marchal alternator had the issue of the red alt light coming on when key is off?

timmy2 · timmy2's Garage

Quote:

Originally Posted by sanandreas

So has anyone with the marchal alternator had the issue of the red alt light coming on when key is off?

This type of failure has been posted before many times in this forum and the best solution is already mentioned in this thread. (Take to a rebuilding Shop)

Most likely a failed diode in the alternator, current is constantly leaking through causing the red light to come on.
Each diode in the alternator needs to be isolated and tested.

Take it to a shop and have it tested and repaired.
Or do a search in these forums and find the diode part numbers to do it yourself if you have the skills.

sanandreas · 03-30-2019, 05:11 PM

I am trying to find someone who has done it themselves on this alternator model. The diode packs on others is quite easy to see and remove. I cannot see them on this unit.

Hoping someone might be able to assist.

Bill Douglas · 03-30-2019, 06:02 PM

There is an alternator place along the Parramatta Road that has seen it all before and are friendly with advice.

Trackrash · Trackrash's Garage

There are some automotive stores here in the states that can test them. Why tear it apart, if you aren't sure if it is bad?

Have you rebuilt an alternator before? I have seen youtube videos on rebuilding these.