Wiring all the gauges in a 911 SC

[woland]

I bought Nine eleven in 2006 aged to 964.

The then-owner put in it also 964 looking gauges but only some of them working:

- The tach (original SC with the plate changed)
- Speedo (original SC with the plate changed)
- Fuel indicator (from 964) with the light switching togheter generator and oil pressure light
- All the other gauges original 964 not wired
- Clock 964 working fine but no signs of life of all indicators



So something happened and I've lost the position of some cable.

With the help of the flow diagram I was able to connect the new clock (brown -; red +; black/blue nightlight);

I found also the cables for tacho (brown -; red/black +; black/blue nightlight) that now works fine;

Direction indicators and high beam are working

Fuel indicator works alone, but when I try to connect other gauges indicates an half full tank.

Now, I assumed that every gauge has to be powered by a (+) red/black cable and by a (-) brown cable. Besides the outlet (G) on the back of the gauges indicates the place to connect the receivers (oil pressure, oil temperature and so).

I tried many combinations of wiring but the gauges rest in peace. No one of them react while giving power, neither turning engine on.

I thought to connect an external cable from sensors to the gauges but I don't know precisely where are those sensors or if something I assume is wrong.

Someone had a similar problem ?

[Gunter]

If I understand correctly, you want to change the wiring back to stock SC ?

For that, you'll need the wiring diagram from a Bentley SC Repair Manual or click on the Tech Info Center on top of this page, then select Elec. Diagrams and find one for SC's.

[woland]

Hi Gunter

of course I have the diagram (911 SC USA Model 81 Part.V) but something is not clear

For instance:
- oil pressure and oil level are two gn/wi cables: no one gives any signal
- in the speedo the re/bl cable seems to be connected with re/bk cable (12V)

in anyway I tried many different combinations without result
if I know where the sensors are in the engine I can proof cable by cable with a
tester. For instance: the small alluminium cup on the right (where are the
engine numbers) gives pression or temperature signal?
In wich position are the other sensors?

[Gunter]

Oil pressure and temperature gauge:

The small pod (Alu cup) next to the engine number is the sender for oil pressure in bars 1-5.
But the 3.0 liter also has a green warning light inside the gauge and that light is operated by the pressure switch located on top of the engine next to the breather cap.

So, you have a switch for the warning light and a sender for the actual pressure.

Oil Temperature Sender is located under the pressure sender pod (Alu cup).

Oil level sender is located inside the oil tank. 2 wires: 1 for 12V and one for ground.

It helps if the wires are still there and have the right color code as the diagram for connections. Brown is always ground on a Porsche.

[woland]

Gunter

You already gave me many useful informations

When you say "But the 3.0 liter also has a green warning light inside the gauge.." you mean a RED warning light or truly green?

For the speedo, the diagram gives me wi/re on contact marked (A) and br/re on contact (31/b) then on (-) contact it seems that brown, br/re and gn cables go alltogheter. Is it possible?

[Gunter]

Warning lights inside the gauge:
Green for oil
Red for Alternator

Speedo:
On contact (-) BRN/RED and BRN come together. BRN/RED is from the Speedometer Sensor and BRN (Ground) is coming from the Tachometer.

On contact 31B is another BRN/RED from the Speedometer Sensor meaning: there are 2 wires BRN/RED coming from the Sensor to the Speedo.

The Speedometer Sensor is located on the 915 transmission and has one BRN and one GRN wire but they both splice into BRN/RED and then go to the Speedo.

All according to Bentley page 970-23

[woland]

No words

Now here is 9:10 PM but tomorrow I'll follow your instructions

Thanks: Paolo

I wonder if my 911 will ever get such a beautiful engine as yours......

[Walt Fricke]

Paolo

The fuel level, oil pressure, oil temperature, and oil tank level sensors are all variable resistors. The sensor wires from the instruments send electrical power to the sensors. All but the temperature sensor are simple windings of resistance wire with a sliding contact.

Here's what the pressure sensor looks like inside:



More than you may need to know. But it explains why you will not measure a voltage, or draw a current, from the sensor itself.

But you should be able to measure a resistance, both at the sensor and where the sensor wire attaches to the gauge. Also, if the resistance is infinite, as when a wire breaks or is disconnected, the gauges, because of their design, will peg - will show the maximum.

Since yours don't do that, I suspect there is an unwanted ground (earth, for those in the Brit tradition) somewhere in the sensor line. Possible in the sensor, but I doubt that. Mine always fail the other way.

There are evil spirits living in these wires, let me tell you. On my car, when I turn on the lights at night the oil pressure drops. Well, the gauge drops. I've checked and checked, and it isn't the headlight draw which does this, because the battery voltage doesn't fall much, and the gauges are designed the way they are so that they are independent of voltage variations.

Buono notte

Walt

[Gunter]

Paolo,

Thanks, that was the original 3.0 from my 1980 SC, rebuild and sold.

I build a Short-stroke 3.2 from a 1982 SC-engine which is in the 911 now.

A SS 3.2 is a 3.0 with bigger P/C's (98 mm instead of 95 mm), a different cam-profile like 964, SSI headers and a flow-through muffler. I like CIS but some people replace it with carburettors.



As Walt says, consider the senders resisting current going through the gauges.

We need a picture of your 911 surrounded by the Alps.

[woland]

Gunter and Walt

I tried to get a picture of both 911 and Alps but today was foggy, so at the moment I'll send you a picture of my valley WITHOUT 911



I searched for a green light in my SC gauge but didn't find it
did you mean this gauge?



I also noticed that some of the lamp holders of SC gauges affect the gauge himself as if it was in short circuit: when I push the general light switch, the instruments jump high.
This not happens if I mount 964 plastic lamp holders with separate ground cable (two contacts, instead one plus metal lamp holder).



Tomorrow I hope to be able to verify if the cables from oil pressure sensor to cockpit are interrupted.

Maybe the "oel druck press" will be so kind to work for me a while

Ciao

[Gunter]

Very pretty pix of the mountains.

About the gauge for oil pressure: Yes, you have the right gauge and it is different from SC's in America. In the picture below, you can see the green light for oil pressure warning.



I like yours better because red makes more sense for a warning light.

Metal casing on the bulb holders is just ground and should not affect the gauge reading when you switch on the instrument lights.
Check carefully for the source of current affecting the gauge. Something is not right.
Electrical stuff can be difficult. Have patience and check each connection to be correct for ground and power.

I like the metal sockets better because they really sit tight and don't fall out.

[Walt Fricke]

Dr. G

Off topic, but can't resist because Paolo's picture triggered the thought.

Many of us have tried to make our instrument lighting brighter. A bit tricky, higher wattage bulbs not easily available from local sources, etc. Do you know if there is greater wattage variety in this later (I guess) style bulb that fits in the plastic holder? I know you don't like that holder, but if I could get brighter bulbs I'd switch.

Or at least do a trial run on one light.

Walt

[woland]

Walt

I heard that the bulbs grow old and that it is sufficient to provide new ones and the gauge lights work a lot better, but I can't find new 2W bulbs in my country and 4W didn't fit in the SC bulb holders.
Another solution is changing the original holders with 964 model, a little bit thinner (you can use a small alluminium strip took from a can to reach the correct diameter).
In the 964-like gauges that I had with the car the then-howner change the bulbs with LED and resistance:



I have done something similar with the licence plate lights using a LED stripe provided of resistance (a resistance each 3 LEDS).
Now they work really fine

[Gunter]

Walt and Paolo,

My 911 is stored in the Winter and during Spring, Summer and Fall I don't do much driving after dark.
A few years ago, I went under the dash to replace burned out bulbs with just regular stock bulbs. I don't know of any higher wattage but I rember that some Pelicans found LED's somewhere (Or even quartz bulbs?) A search on this board may give some more info.

Very nice color, Paolo. Do you actually drive in the Winter? Not worried about Salt?

[woland]

Gunter

I passed winter 2008-9 driving an Audi cabrio. It was terrible so i decided to use 911 every day this year. I have to look for salt and keep it washed everytime it's possible but I didn't risk that CIS decide not to rise up from hibernation

This afternoon I controlled the two cables coming from the oil sensor: I took a 3,5 meter long cable and stapled it with sensor cables in the engine compartement.




Then I went in the car to test if they were interrupted at some point.



Tester went from 1 to 0 with both re/gn and bk/gn so I connected the temperature and druck gauges after cleaned and deoxy the contacts.
There will be something strange because the druck gauge didn't moves from 5bar either the engine is stopped or runs.
Tonight I had a too short path coming back home so I think that oil temperature is working but I'll be shure only tomorrow morning
Ah! With the oil gauge connected, the fuel level didn't work at all.....

[Walt Fricke]

Paolo

Whenever the oil pressure gauge (or the oil level gauge) pegs at maximum values, it is because there is a break in the sender system. If it is not the wire connecting to the gauge, then it is in the sensor itself. You can easily test this at the gauge with an ohmmeter, which I see you have. I've got some values somewhere, but if the ohmmeter reads infinite resistance, the sensor is shot.

You can confirm this easily. Ground the sensor terminal of the gauge. It should be at the 0 or rest position. Hook up the sensor wire, and ground that wire back at the sensor. Again, should be 0. Actually, the gauge should move just a little bit when you ground the sensor connection - from below 0 up a bit to 0.

If your gauge does not do this (when properly grounded and fed 12V to those terminals), then the gauge is bad. My experience, such as it is, suggests that seldom (if ever) are the gauges bad. The pressure senders do go bad, as do the oil level senders. Sometimes the fuel level senders go bad. I think the temperature sensors may last forever, as they have no moving parts inside to wear or break.

Walt

[Gunter]

Ah! With the oil gauge connected, the fuel level didn't work at all.....

Some wiring is not connected properly behind the dashboard. I remember you saying that the gauges are affected when you switch on the dash lights.

Check each gauge for the right wiring using the color code from the diagram.

Test the gauge and the sender as Walt is suggesting.

There are a few different ways to check components. Think about how the current is supposed to flow. Most gauges work on the principal of power to the gauge (+) and the ground connection (-) going through a variable resistor (Sender) and then to ground. The sender limits the amount of current and that limit affects the reading (Needle) on the gauge.

To test gauges:
The ends of the wire-connections are Faston-types. Make up 2 extra wires about 20 cm long and crimp on the Faston-female conectors, one end only. On the other ends, remove about 10 mm insulation.
Connect the 2 wires + and - to the gauge and to the battery pos. and neg. terminals respectively. The needle should go to max (5)

Testing gauges with the extra 2 wires right from the battery leaves the resistor or (sender) out of the circuit.

Test the sender with the OHM meter. Disconnect the wires on the sender. Remember that OHM is measured always with no current in the wire, or part, you're testing.

By testing the parts independently, you'll find out if the gauge or sender is good or bad.

If the gauge and sender appear good, the next step is to find out if the wires in the dash have power for the gauge. When you turn the ignition ON, do you have 12 V in the RED/BLK wire for the gauge? My diagram shows RED/BLK as + for all gauges. Is that the same on your diagram?

Connect the gauge to the right dash wires but DO NOT connect the instrument lights. Just the correct 12 V (RED/BLK) to the gauge and the neg. wire to the sender.
I understand that you see 5 bars (Max) when you have the gauge in the dash? That means there is a break in the wiring to the sender or the sender is bad. Most likely something with the wiring.
Connect the wire on the sender. The sender is just a variable resistor.
Turn ignition ON. The needle in the gauge should go to rest (o) if the sender is good.

If the gauges are wired correctly and work, you can connect the instrument lights and see if it has an effect on the gauge. If there is an interference, you have something wrong with the wires for the lights.

Have patience.

[woland]

Hi

I verified that every gauge reacts when I apply current to (+) and (-)

I also verified that when I turn the ignition ON, I have 12 V in the RED/BLK wire if I test it togheter with brown (-) wire, BUT:

- If the clock is not connected when I turn ignition OFF the tester give me 0
When I connect the clock with the only positive wire that works in every ignition position, then turning ignition OFF I find a 2,5 current flowing through the red/bk wires. I wonder if this fact is normal or if the clock is in short circuit unless it marks time correctly.
Is there a way to verify if the clock is shorted?

- Having only 3-4 (red/bk) 12V wires working with ignition ON and the same for the negative brown wires, I made a multiple connection with the fastons to connect 6 gauges (+) and 7 negative (gauges+clock). So every double gauge has a bridge giving power to the male fastons in the instrument.



At the moment I only know from where oil pressure and oil temperature wires are coming and I know that they are integers. I tried to find where is the pressure light sensor, but I didn't recognized something like a bulb.

I have disconnected the bk/blue wires of lights to avoid further confusion
Tomorrow I also will try what Walt suggests grounding the G of the gauge.

Thanks to you all and see you tomorrow

[Gunter]

Bon Giorno, Paolo.

The clock has only 1 + and 1 - (ground) connection plus one light bulb.

Leave the light bulb disconnected.
Test the clock straight from the battery with short extra wires.
Connect the + and - to make the clock run. It either works or it doesn't.

Notice that the - (ground) connection is the actual body of the clock.
The connection for the light bulb also has the body for ground.
If there is something wrong with the wiring for the instrument lights, it will interfere with correct working of the clock (Or other gauges)
Look at the power distribution and notice that the clock is inline with many other electrical components. Any short in the other devises (Or any short in the instrument lights) will have an effect on correct operation of the gauges.

Make sure that ALL fuses are good!

Here is a picture showing the red switch on top of the engine for the oil pressure light inside the oil pressure gauge:



It is a simple switch providing ground for the warning light when you turn ignition ON. As soon as the engine runs, the oil pressure in the engine opens the switch and the light goes out.
The switch has only 1 wire and is situated next to the breather cap on the engine. Follow the big hose from the oil filler pipe to the breather cap.

When tracing electrical problems, each component is tested individually outside the circuit to make sure they work.

[woland]

Hoping to have done a good work

After lunch I went to see what the clock fuse protects and found that only the clock, hood and trunk lights togheter with the internal light work with this fuse.

I verified that removing the fourth fuse the clock is off, the I went to verify the trunk light: immaculate but didn't found where the switch is; engine compartment light: absent; internal light on the roll bar (Targa) verified contacts sprayed deoxy: it works and didn't affects the Ohmeter.

Then I made the experiment with gauges: connected with a battery charger the needle go up; when I ground it the needles fall: they work (I bought all the gauges and clock in Ebay from 70rsr and he always sent me VERY nice items - today my new front blower arrived from him).



Then I verified all the cables in the cockpit, fixed the fastons with their plastic caps and connected tach and clock and direction arrows.

Tomorrow I will organize the wires for groups. One group for each gauge.

I'll let you know the matter