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Discussion Starter · #1 ·
I am out of ideas. My GT oil pressure gauge has not been right since I built the car. I am on my third set of senders and gauges. The wires have been checked from one end to the other. It all seems to work backwards, gauge goes negative with pressure. Tonight I pulled a known good sender and gauge and hooked them up without a car. Put pressure to the sender and the gauge goes minus. I tried different ways of wiring it and it either works backwards or not at all. Any ideas at all would be helpful. Electronics is my specialty and it makes no sense to me.
 

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more info?

Does the guage go linearly with a change in pressure? I mean, does a small change in pressure give you a small change in needle, and a large a large and such, and all backwards, or does the guage go suddenly from one end to the other?

If it is happening suddenly, it may be that you're trying to use the wrong terminal on the pressure sender. One is for the idiot light (it will read 0 ohms or so to the case with no pressure source, and then get very high at @15#) The other is for the guage. The guage terminal will have a change in resistance with every change in pressure. The kicker is that both wires are the same color and size going to the sender.

If it is happening roughly in response to the change in input, you may have the terminals on the guage reversed. It seems to me swapping terminals around would give you the same effect.
 

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Discussion Starter · #3 ·
The gauge moves very evenly with pressure in a minus direction, or positive with vacuum. If I hook it to the other terminal on the sender it pegs positive with no pressure. I am wondering if there is something missing in the wiring. The prints show it just like I have it hooked up.
 

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I'm going to go with "Old Opel Guy' on this. The schematic shows a black/red wire powering the Fuel/Temp/Oil Press gages. The Light Blue/Green wires ground the Oil Press Gage through the sender, one for the gage and one for the light It appears that the wires at the gage are hooked up backwards from what you've described. HTH.

Ron
 

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more looking

All right, so you have the sending unit and the guage both out and in your hands, wired up as follows:

-12V(+) hooked up to the (+) terminal on the back of the guage.
-12V(-) hooked up to the guage case, the sending unit threads, and the (-) terminal on the back of the guage.
-A wire connecting the "G" terminal of the guage to the "G" terminal of the sending unit.
-A light bulb wired between the 12V(+) and the "WK" terminal on the sending unit

And when you apply power and pressure the guage goes the wrong direction? Does the light go out?

Very odd....
 

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Discussion Starter · #6 · (Edited)
Yes everything you said is true, no the light doesn't go on either. And I agree it is very odd. That is why I tried it without the car as a variable. I have also looked through all years wiring diagrams and they are all the same. It is kickin my butt. I think it will be hard to get used to the idiot light on and gauge below 0 as a good thing.
 

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my bet on the idiot light part of the problem is that the wire from the "WK" terminal on the sender to the receptacle and the fuse box is toughing Ground--somewhere. That would keep the light on.

Needle going backwards: = and - must be reversed on the hookup. Here is the whole circuit:
 

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Discussion Starter · #8 ·
The thing to keep in mind here is that the gauge, sender, power supply, pump and a handful of jumpers are on a table, the car is outside. If you reverse polarity, case and sender hot, nothing works. If the idiot light and gauge wire are reversed the gauge shows full pressure and idiot light is really cool, has a dimmer effect with pressure. I can see all connections at a glance.

I have oil pressure above the filter on the car. However I have decided to cut this marshmallow with an axe. As soon as parts start arriving I will be taking it apart. I intend to start in the front of the engine and continue dissmanteling until I find the problem or the firewall.

As for this sending unit I intend to treat it like a solex. I think I can do 30 to 40 yards easy.
 

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What are L and B on the wiring diagram near the top? I know the Manta has a voltage stabilizer that plugs into the back or the guage panel. I have replaced several, they can do strange things.

DAN
 

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Discussion Starter · #10 ·
L & B are the two connections for the amp gauge. Just off the top of my head would say line and battery.
 

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Discussion Starter · #12 ·
This is the dual type that is used for the GT. The PO lost the one for this car, or I didn't get that box when it was moved. It was a box case, as in too many parts for a basket. Last two PO's worked on it to restore but got nowhere.
 

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A lot of guages (except amp/volt) dont run on a full 12 volts, they have some kind of voltage limiting device somewhere. I do not have my wiring diagrams with me right now but will look it over when I can. Just thinkin over your trouble maks me wonder if that could be the trouble with your guage, too much voltage, guage would read high, right?

DAN
 

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Lookin thru the diagrams on this site I see that the black and red wire to the guage comes from what looks like a 3 pronged device(un-named). This could be the voltage stabilizer(limiter?). It looks like it is wired to almost all the guages. Too much voltage to your guages? That would also explain why your bench tests are not getting anywhere. It looks like the Blk/red wire comes from the fuse goes to the limiter then to the guages, diagram a little hard to make out.

DAN
 

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Discussion Starter · #16 ·
The point on the prints you are looking at is a common or junction point for the 12vdc +. I snipped a couple of bulbs off another dash and the black/red is parallelled on one of them, would look like a splice or junction on a print. The problem I see with this one is the change in potential is reversed. I can watch it with a meter, with no power to it. It also appears that the idiot light contacts have opened, as in for good.
 
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