Blue wire circuit syndrome

[Miego]

Hi all,
Just subscribed to this forum. Can’t seem to complete my profile, but FYI: living in Belgium (Europe), so Dutch is my mother tongue (so please bear with me). Owning a ’80 SC (188 HP) for almost 20 years. The car is in fairly original shape but has undergone some major work to engine and body and is maintained by a local specialist. Fairly happy with their service – car is doing great with around 230K (km) on the clock.
However over the last 3 years, it is suffering from the blue wire syndrome (61). On just a few occasions, really randomly, red warning light comes on – only dim – and then goes out again after 15-20 min. When measuring with the light on and engine running, battery voltage is within spec. Read plenty of info on the internet, as various posts on this list.
I measured resistance over that blue wire circuit and get 1,1 Ohms, which is probably too much. In my search to trace that resistance, I have 2 questions:
- Wiring near the regulator plug clearly shows a blue wire. The wire reaching the bulb however is blue w/ green stripe. Just behind the cluster though is a blue wire with a connector which clearly has seen higher temperatures; one of these wires also is connected to the blue wire circuit, but still measures 0,9 Ohms. Hope you guys have an idea where the blue wire is connecting with the blue/green one and what it’s purpose is? Replaced 3 connectors parts – no improvement.
- Wiring diagrams an posts refer to two 14-pin connectors. One is easy to find behind the plastic cover in the engine bay, but where is the second one? Or is diagram just referring to 2 halves of that same connector?
To compete the information: alternator has been rebuilt some 10.000km ago, regulator is a new solid state one, but the problem occurred with both the original and the new one.
Thanks a lot and I hope I didn’t offend any rules!
Filip

[lrodri64]

Hi,
You should replace the alternator carbon brushes,
Regards.

[Miego]

Hi lrodri64,

Thanks for the feedback. Was actually hoping that those would have been replaced when they overhauled the alternator, but one never knows ... Before diving into the alternator itself though or handing the car back in at the shop, i was hoping to sort out the evident electric issues related to this problem.
Maybe have to add that i measured that resistance between the connector (3 blade one) of the (external) regulator and bulb holder. So not the part between the RR and the alternator.

Might as well throw in a picture of the car: oakgreen original colour (repainted at some point), original brown checkered flag interior. Original 3.0L engine.

Thanks
Filip

[Miego]

2nd attempt to post picture

[targa80]

Looking at the 81 schematics that I use for my 80SC Targa the blue (bl) wire is tied to the blue/green (bl/gn) at the gen light. The bl/gn is tied to contact 61 of oxy mileage counter. The bl wire connects to factory alarm behind tach and also passes through connector T14-11 located on regulator panel in engine bay. T14-11 bl wire connects to regulator D+ terminal and generator D+ terminal.

[Miego]

Interesting leads, thanx. Could you maybe share that wiring diagram targa80?
On the other hand i don't think we have an O2 mileage counter here in Europe spec 911's. And i've never heard of a factory alarm either; at least it never sounded in my car :-)

The blue and blue green are joined together in a common sleeve, and seem to be running towards the right of the dashboard, so towards the mileage counter (or further down? Maybe have to pull that one out too to check the connections or to get a view on the wiring as access from the trunk is blocked by the ventilator assy.

Also, according to some drawings, the blue wire has 2 connections at the RR: one for the alternator, one for the warning light. I can only see one 1 blue wire at the RR though.

So my guess is that this one wire runs to the front of the car, and is split in bl and bl/gn sowhere behind the dash. That is probably where i get the resistance.

Can these wiring diagrams be purchased somewhere?

[targa80]

Midtown,

PM me with your email address and I will send it. I have been having issues with my internet upload so it may fail to send I will let you know. If you have a factory alarm there would be a lock on the inside driver door. Just open your drivers door and look on the upper edge above the door latch mechanism. The oxy counter was a part of the O2 sensor circuit used with the lambda kjetronics CIS fuel injection.

[timmy2]

1978 diagram in the link. The blue green wire likely isn’t used on your car. (ROW without Lambda) but the wires may be there as Porsche included all options in their harnesses, just left off the devices.
Check continuity from the blue wire in your photo to the remote VR connector (3 pole plug) that is beside the CDI box at the fuse panel with rear 14 pin connector of the engine harness plugged in.
ROW cars only have the blue wire and the red black wire (gauge power) to the Generator lamp.

https://www.dropbox.com/s/yjfoxfvwlci6lys/911_electrical_78SC_USA.pdf?dl=0

[Miego]

Timmy2, thanks for sharing!
After reading your posts and looking at the diagram, still remain puzzled as to where the bl/gn connects with the blue wire and why there are 2 wires.
Resistance on the plain blue wire circuit is 0,9 so just slightly below the 1,1 measured over the bl/gn, but still high. The blue wire is thicker than the bl/gn which is only about 0,75mm²; that could explain the 0,2 difference.

Guess i will have to dig in that dash a bit more...

So there is no second 14 pin connector either?

[timmy2]

If you have no alarm and no Lambda for O2 counter, then you likely just have terminated wires there. (They lead to no devices)
No second 14 pin connector, just the male one on the rear fuse panel and the female one for the engine harness.

[Miego]

Merry Christmas to you all!

Have to correct myself here: the blue wire to the bulb is obviously not a blue/green one (as in the picture that targa80 posted some time ago), but a blue/red one (as can be seen on my own picture).
Some more measurements on my cheapo multimeter: from regulator blue to female 11 pin: 0,6 (just above the 0,4 shorting the meter). So that part of the wiring seems quite OK.

From male 11 to blue behind the gauge: 0,7. From male 11 to blue/red (control light) is still 1,1. So measurable resistance, difference might be due to cross section. At the time my workshop suggested to swap both wires just to try, but i'm not sure what feeds the plain blue circuit, but it surely has seen some heat (see picture); so swapping to smaller cross section might not be the better idea in the long run.

Still trying to locate where both circuits meet. Where is the O2 sensor counter originally located?

Thanks all!

[targa80]

Looking at timmy2’s schematic I could not find a blue with red stripe wire or red with blue stripe wire anywhere. The 81 schematic has a red with blue stripe wire that connects from ox warning light to gen charge light along with two red with black striped wires. If the car is ROW an did not have emissions required hardware such as lambda/ catalytic converter with CO2 sensor then you would not have the oxy light or counter. You will need to decide which schematic matches your setup to isolate the circuits you are concerned about. As timmy2 said you may have wires that are in the bundles but are not connected due to lack of emissions hardware. When I was methodically going through my wiring I had the 79 schematic and the 81 schematic. I have never found a complete 1980 specific schematic. My cars electric matched the 1981 schematics with addition of a 1980 oxygen sensor circuit.

[timmy2]

The only page in the factory manual for the 1980 schematics after the ‘78/79 drawing that I linked to, is the 1980 lambda schematic.

[Miego]

Just a small update for those interested. Ended up handing the car back in at the workshop in a last attempt to get rid of the glowing alternator bulb, without replacing the entire alternator. On my request they replaced the brushes (small cassette) and the ground wire(s) behind the alternator to the crankcase. They also made sure the wiring behind the dashboard was all hooked up as should be. BTW, the extra blue wire seemed to be for a (not installed) O2 sensor as was mentioned here.
Result: no resistance on the wiring anymore, battery still charging perfectly but light still glowing...

For the record: this is a Marchal with external regulator. And as i understand from some additional research, it is equiped with a set of diodes, just to feed the control light and thus matching (or not) the output of the rectifier. In other words: leaking diodes. Could be, as the problem popped up for the first time some 4 or 5 years ago, only getting more frequent over the years and finally resulting in a steady glow.

As that light annoys me, my plan is to replace the alternator with a new one from for instance Valeo (same type, keep the external regulator). Costs around 350€ without labour. The Bosch remanufactured version sadly only seems available in the US, not in Europe.

Filip

[911obgyn]

The charging wire to the starter, red, should also be checked for high resistance or burning. Some have green corrosion inside the insulation.

[cassisrot]

I’ve found that little stickers sized to cover the annoying warning light would save you a bunch of euros.

[targa80]

Originally Posted by Miego

……………

For the record: this is a Marchal with external regulator. And as i understand from some additional research, it is equiped with a set of diodes, just to feed the control light and thus matching (or not) the output of the rectifier. In other words: leaking diodes. Could be, as the problem popped up for the first time some 4 or 5 years ago, only getting more frequent over the years and finally resulting in a steady glow.

As that light annoys me, my plan is to replace the alternator with a new one from for instance Valeo (same type, keep the external regulator). Costs around 350€ without labour. The Bosch remanufactured version sadly only seems available in the US, not in Europe.

Filip

Besides the main rectifying diodes in the alternator their are three exciter diodes.

Over 17 years ago I had the charger light glow at idle and go out as RPM's were increased. Troubleshot the problem down to the three small exciter diodes in the alternator. They disintegrated as soon as I touched them from years of high heat. Bought a pack of 1N4000 diodes from Radio shack and soldered them into the mounting circuit board in the alternator. The 1N4000 are a general purpose diode and they are still working today. while I was in there I changed the bearings and brushes. For me it was a very cheap fix vs buying a new or reconditioned Marcel alternator.

The exciter diodes provides the voltage feedback to the voltage regulator. A loss of an exciter diode will cause the charge light to glow at low rpm’s due to loss of some of the feedback signal voltage.

Recently, I upgraded to Classic Retrofit 175 amp alternator with the Electrocooler install.