Gauge wiring

[occb2]

Hi all. I did the white face gauge change on my 1985 911 Targa. I did a sketch of the wiring and put everything back the way it was or so I thought. The problem I am having is that two days after doing that, my Oil Pressure gauge pins at 5. I did a search and it seems like a bad ground. I would assume that is was from me changing the faces.

I have two questions. The first being. Does anyone have pictures of the back of their gauges with the wires still attached for a 84-89 Carrera?

Also, how hard would it be to run a new wire from the pressure sending unit next to the fan to the gauge and what else would that entail. Thanks.

Robert

[78targa]

It does sound like the gauge signal is grounding out.

I always diagnose issues using the: "Whatever you worked on last is most likely where the problem occurred" approach.

I would check to make sure that you put all of the wires on the Oil Pressure gauge back properly.

There is a cluster of three prongs on the back of the gauge that can be easy to get confused with. Make sure the sending signal is on the spade marked "G" It is very easy to think this means "ground". It isn't. The ground spade is marked with a series of decreasing hashmarks, like a pyramid.

The two gauges (oil temp and oil press) are also wired in mirror to each other as I recall.

Make sure you look closely with a flashlight. At least you didn't get the power on the wrong one or you would have blown a fuse.

Running another wire to the sender would be a big hassle and besides, I doubt that is your issue.

[occb2]

Today I got to work on it alittle more. I disconnected the wire on the oil pressure sending unit. I thought that it wound make the gauge drop to 0. It didn't. I also grounded the wire and it still didn't drop the needle. When I shut the ign. off the needle drops. I just put the ign, on it peeks to the 5. When I get home at 2 am I will look again. I'm almost 100% I put it back the way I took it off. If I remember it was green red then the othe side was red green. Then the Ground went to the pressure gauge on the tab with the strange symble on it. But I'll check again.

Anyone have pictures off all the back of their gauges with the wires still on them. I see the one for the tech on how to change to white face gauges but the year of that car is different. Thanks again.

Rob

[78targa]

Well, if you have the ground wire on the gauge spade terminal, it would do what you are describing.

I don't have a camera with me right now, but I can tell you the terminals look like thisif you were looking at the back of the gauge:

gauge | | Positive

Ground ____


The positive spade is to the inboard side of the gauge

[occb2]

I'm thinking it might be another gauge that is not wired up right. Can't for the life of me figure out the electrical wiring diagrams in my Bentley manual. But I see in some strange way they are all hooked up together.

The way you posted the connections is the way I have it.

Ground
_
Greeen I I RED RED I I GREEN
_
Nothing

That is the way, off the top of my head, how it is connected. I'll know more at around 2AM when I get home.

Robert

Still would love pics from an 84-89 911 gauge connections if anyone has them. Thanks again.

Robert

[occb2]

Here are pics of a good set of gauges. I went to my friends Porsche shop and looked at a 85 that was there. I will try to upload them.

[occb2]

Ok. My wires are fine and I changed my sensor. What else could it be. Is there a way of wiring just the Oil pressure sensor? Like a direct lead to the sensor and then a ground? All other gauges are working as they should. Oh and its not the unit itself because I put in another gauge set and it did the same thing. Can't figure this out. Any help would be great.

Robert

[78targa]

I went back and looked at your second post.

Did you indicate that the ground wire was on top? I am under the understanding that there are only three prongs on the oil pressure side and the prongs make a "U" shape.

The gauge wire is to the outside, the positive is to the inside and the ground is on the bottom.

Are you sure you have it wired right?

If you are certain that you have everything wired correctly and you have a good sensor, then you would have to assume you have a bad gauge. If you feel it necessary to change the wiring from the sender to tha gauge, you could do that as well.

Run a wire from the sender, through the tunnel and to the gauge. The harness for the ground wire should be fine or else all of your other gauges would not be grounding properly.

The odds are immensely small that the wire has gone bad, but if you think that is your solution, then I guess running another wire would work.

[occb2]

78Targa. Thanks for the advice. I'm sorry with the 2nd post. The gauge goes green, red on the Temp and then red, green on the oil press. The brown wire is on the top of those on the oil press side. The gauge wire is the brown? From the car I looked at it is wired right.

Do you think I grounded the (+) on the gauge and fried it. That would make it a dead wire causing the ground to cause the gauge to spike.

So tomorrow or maybe monday, I will run a new wire from the gauge to the unit. I will put it on where the red wire is. Also ground would be the Brown wire. What is the green wire? Thanks.

Robert

I Have a bentley manual. I'll read it tomorrow morning. I think it showed one wire, red or green going to another gauge.

Robert

[marks914]

Sounds like the ground and sender are backwards

Mark

[scarceller]

Here's a though to test the guage and sender:

1) Take the gauge out of the dash
2) Power and ground it with test clips at the engine bay, obtain power from one of the 3 fuses on the left rear of the engine bay then connect a signal wire directly from the sender to the gauge.
3) start car see if gauge works

This way you would eliminate all the wires with known good ones and could prove 100% that the gauge and sender are functional.

Would take a little time to get 3 jumper test wires with alligator clips (Walmart or RadioShack) but would be worth testing.

[scarceller]

OK, I just checked my gauge in my 84 Carrera:

Looking at the gauge from the rear the top post is ground, the left is 12V, then the right one is the green signal wire.

Then with key in run and the green signal wire disconnected the gauge sits at 0.

Then key in run with green signal wire disconnected I jumpered the signal post to ground and the gauge pegs as you suspected.

So if you have ground on the top post, 12v on the left post and the right signal post is disconnected and the gauge is pegged you have an internal issue within the gauge. Simply if the gauge only has power and ground it should NOT be pegged.

Hope this helps.

[scarceller]

I borrowed this pic from above and marked it up for you:


This picture seems a little wrong as the ground post in this picture is not connected to ground? In my car it looks exactly like this but that ground post has a few (3 or so) ground wires on it. I know the fella mentioned taking these pics from a working set, but maybe the ground got unplugged when he pulled the gauge out? I do not think the gauge will work without that ground post grounded.