No warning lights with ignition on - what to do?

[thobri]

Hey guys

Car is a '74 with a '87 3.2....

I just had my gauges overhauled and after installing them again a friend told me that the oil & alternator ligth in the oil combo gauge should be on when ignition is on. They are not and was not before overhauling the gauges. Dunno why I never noticed this? I always pays attention to the oil pressure indicator with engine running, which is fine. However, a few times before I have noticed the red alternator light on after starting the engine - but only till you rev a bit, then it's gone... (Guess I mistook this as the oil warning light like many others since it is red!) I really cannot say for sure if I ever saw the green oil lamp on - but I checked it by removing the green/white wire and give the light ground - then it is on with ignition on. So the bulp is at least working.
I have a loose green/white wire that I don't where belong - it is not connected to the other green/white wire connected to the oil pressure light?

I am going to find the oil pressure switch and measure if the wire is the one connected to the gauge. I know it might be the switch that is gone which I really hope not since the engine was out last summer!! Done by a classic Porsche mechanic - so I guess it should be fine?!?

Apart from this I don't know what to check - any good ideas?
If there is connection from the wire at the switch to the gauge - is it the switch for sure?

Bonus info: With ignition on the brake-light is blinking when handbrake is pulled, and the oil pressure indicator goes to 0 as it should. But nothing in alternator and oil pressure idiot lights.
I am pretty sure everything works once the engine is running (at least the alternator!) so my theory is that something is not connected right to make it work just with ignition on.

I will check the connectivity from the wire at the switch (if I can get to it) to the gauge later today.
Any other good ideas?

Thanks for your time.
Tom

[T77911S]

with an engine swap I think it may be a crap shoot for us to really help. timmy may be your best bet.

I would start with grounding the wire at the sending unit and key on to see if the light comes on.
if that does not work (based on 77 14 pin wiring diagram) I would try grounding pin 9 of the 14 pin connector in the engine bay. if still no go I would take a look at the gauge wiring since you have had them out.

if the alt light comes on after starting and goes off if you rev the engine it may be working but I would verify with a MM on the battery. you want at least 14v.
I think there was a mod for a diode to fix the alt light and reving the engine thing.
the alt light should be on with key on and engine off.

timmy or someone that has done this engine swap will be of more help.

[timmy2]

One green white is for oil pressure idiot light, the other is for oil level gauge.
Oil pressure idiot light green/white comes out of vinyl harness bundle behind the gauges with oil temp and pressure and alt lamp wires. (Green/black, green red, blue, the brake lamp wire and a spare green wire)

Oil level green/white wire comes out of the same harness a little further back with the black/purple tach wire.
Hope that helps you to figure out which one goes where.

[timmy2]

Looks like this, oil level green white is longer and is in top left of photo with the purple black splitting out of harness earlier.
Oil pressure green white is in the bundle of other wires.

[thobri]

Hi Dennis & T77

Thanks for help - much appreciated.
I will go into the mans cave tonight and give it another go...

Thanks again - have a great day.
Best Tom

[thobri]

After tonight a little update...

1. Could not measure any contact (with a multimeter) from the wire at the oil pressure switch at engine to the green/white wire at the gauges. Damn, so I guess this explains why there is no light. Any place where to look/measure - or would you guys recommend to draw a new wire from the switch to the gause (Danm...) Still don't know if the switch works - looks dry so no leaking - but it is not new so the mechanic did not change it while engine was out ... (DAMN...)

2. Seems like the wires at the dash is connected correct.
Dennis wrote:
One green white is for oil pressure idiot light, the other is for oil level gauge.
Oil pressure idiot light green/white comes out of vinyl harness bundle behind the gauges with oil temp and pressure and alt lamp wires. (Green/black, green red, blue, the brake lamp wire and a spare green wire)
Yes, the green/white wire for oil idiot light comes out of harnesh together with: brown/yellow, green (extra), blue, green/black and green/red.

Oil level green/white wire comes out of the same harness a little further back with the black/purple tach wire.
Yes, it is there and connected to the oil level gauge.

However, I still have an green/white wire! It comes out of another vinyl harnesh together with 2 x red/black and 1 x brown/yellow. These wires have the second color across the wires - where the other wires above have the second color along the wires. (if this makes any difference or sense?)

I guess it can be due to another wiring harness than the original '74 car when they installed the 3.2 engine... But still - perhaps it makes sense to someone...

Guess my next move is to draw a new wire from the switch to the gauge - just outside the car to begin with to see if it works...
Does it make sense?

Thanks :-)

Best Tom

[timmy2]

Check the 14 pin connector at th rear fuse panel for continuity from the sender to the female terminal connector. Pin 9 I believe.
Pop the cover to be sure. Then from the corresponding male 14 pin connector terminal to the green white wire at the gauge.

[timmy2]

Green/white or white /green?
Here is a link to your original wiring schematic for your '74.
https://www.dropbox.com/sh/s292jtsyvl6llw2/AABF-ofgMfoMltGa99Asphr5a?dl=0

[T77911S]

according to the diagram timmy posted I don't think this goes thru the 14 pin connector,
the diagram says a SINGLE connector located near the relay panel.
if so, use that for the tests.

you can use a test light.

clip the lead to one of the fuses in the engine bay then ground the light and make sure you have power. (light on).
test the pin on the connector that goes to the engine. if the sender is good the light should light.

clip the TL to ground, turn on the key and check side going to the light. light should light.

the other side of the light goes to the seat belt warning, I wonder why???

the idiot light and gauge get power from the same place. if you can verify power at the light that would be good, also verify bulb works,

I would unplug the seat belt warning and see if that does anything,. you can also check for power at pin B, maybe even ground it to see if the light comes on.

[thobri]

Thanks guys - I will give it a go...

:-)

Best Tom

[thobri]

So good news...

Made a dummy wire from the switch to the gauge.

- with ignition on = it turns green (yeahhh)
- with engine on = it goes out (hell yeahhh)

So far so good... Happy to learn the switch is working.

Checked the 14 pin connector. I have connection with the green/white wire from the switch at the connector (at the engine side).
But it seems the pin is not in the right pin.
At the other side of the connector (at car side) there is a black/purple pin at that spot.

Can't see a green/white wire at this side of the connector clearly - afraid to take all out (guess I need to and make a drawing of which colors goes where...)

However, I did find a loose green/white wire 5 cm from the 14 pin connector with a female connector - well taped away... Felt lucky and made a connection-test to the green/white wire at the gauge - boom - connection. So if everythings else fails I can draw a wire from the switch to this wire and the oil idiot light will work. But - naturally I prefer to do things right. Also, I guess that there's a good chance that if I get this 14 pin connector right maybe my alternator idiot light issue will also be fixed...

What do I need to do now? I am a bit afraid to fizzle with the 14 pin connector since all my other gauges work (so I guess it cannot be totally off)... What do I need to take care of...

Any final tips?

Thank you in advance guys - you've been very helpful.

Best
Tom

[timmy2]

PM or email me with your phone number and a good time to call.
I'll help you troubleshoot what you have.
Be prepared to send email or text photos while we talk.
(I get home around 6 pm pacific time from work)

[timmy2]

Yep, '74 has a single terminal connector near the fuse panel for the oil pressure idiot switch.
I was thinking of later years for it being in the 14 pin connector.
'74 is a real unique year for wiring..... Porsche was still
Figuring out what they wanted to do!

Should be a male and female connector for green/white. One female in the harness coming from the engine, one male with plastic cover near the 14 pin connector at the rear fuse panel for it to plug into.

[T77911S]

I almost posted this yesterday.
I did not make this up.
looks like it might be for and engine swap.

[thobri]

So time for an update...

Took the green/white out from the 14 pin connector and connected it to the single connector at the rear. Cleaned the blue wires in the 14 pin connector to see if this could be enough to make the alternator light go on with ignition on.
Good news - now both the oil pressure idiot and alternator light is on with ignition.

However, now all my gauge lights are out...

Seems it is always one step forward and one back when you deal with old electric wiring...

Can't find any loose connections - changed one blown bulp but still - all are out...

There are no blown fused in the front panel - any ideas where to look?

SO close to the goal!

Best
Tom

[l_turn9]

Excellent thread! I plan to check out why my green oil light no longer works once I finish some other chores. Speaking of the 14 pn connector near cyl #3 = can someone point me to the page in the Porsche Parts Catalog where this appears? Thanks!

BTW, if anyone wants a Porsche (Factory) Parts Catalog, follow this link: https://www.porsche.com/usa/accessoriesandservices/classic/genuineparts/originalpartscatalogue/
Than scroll down 1/4 of the page and select your year/model.

[l_turn9]

Not sure where I found these (maybe Pelican Forums?) but they will help someone - I prefer the color diagr but the other diagrams may help someone - I like the top diagram but one is for the Turbo.