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Old 06-07-2021, 10:08 AM   #1
VB242
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Default 5 bar oil pressure gauge wiring

I know there was just a thread about this but I can't find it. I have power going to the gauge, when I hook up the one terminal on the sender the gauge jumps a little then sits on 0 psi. If I put it on the other terminal it pegs out below 0, could I have the power reversed? I got the gauge and sender from pick and pull so I don't know if the wiring is factory. I have + going to blue/ red wire and - to the black wire and green coming from the gauge terminal.
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Old 06-07-2021, 10:32 AM   #2
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OE 52mm gauge?
Looking at the back of the gauge:
-12v to the bottom spade terminal
-ground to the side spade terminal
-sender connection to the top spade terminal

How is your sender connected at the engine? Does it have a good ground to the block (no sealant on threads)?

Also FWIW, the 5 bar gauge I have needs a tap or two with my finger to "wake up" when the car is first started.
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Old 06-07-2021, 10:51 AM   #3
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I checked for good continuity to the block for the ground, I'll check and see how the wiring on the gauge is connected.
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Old 06-07-2021, 04:00 PM   #4
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Which sender do you have?

The dummy light sender which comes stock won't work with the 5 bar gauge, you need the big cylindrical VDO sender for it.

Here's the recent thread:

https://forums.turbobricks.com/showt...15#post6190115
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Old 06-07-2021, 04:07 PM   #5
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They also make different sensors for different ranges, make sure you got the right PN
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Old 06-07-2021, 10:18 PM   #6
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They also make different sensors for different ranges, make sure you got the right PN
I got both parts from a junkyard car, it's definitely a gauge sending unit, it's got the G and W terminals. No chance to mess with it today had to get a free warranty battery from Walmart for the 780 and also put some a/c repair in.
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Old 06-08-2021, 09:40 PM   #7
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Wiring appears correct, the letter markings on the sender are hidden by the heater pipe. When I put it on one terminal i get 0psi when I put it on the other I get negative psi. Maybe it didn't work for the junkyard car either. When I put it to KP2 the needle jumps up to 0 from resting.
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Old 06-08-2021, 10:57 PM   #8
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They also make different sensors for different ranges, make sure you got the right PN
I know they have a 3 bar, 5 bar (80psi-ish), and a 100psi one. With a couple versions of each with different resistance ranges.

All of them should though produce some activity on the gauge even if the gauge/sender combination is wrong.

Have you got some resistors on hand to test the gauge with? The sender is really just a variable resistor between the gauge and ground (the engine).
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Old 06-08-2021, 11:29 PM   #9
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G should be to the gauge (sending unit portion) and W should be for the warning light (switch). I'm sure you could find a chart of resistance values vs pressure and check between G and ground, if its within spec its probably the gauge.
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Old 06-08-2021, 11:39 PM   #10
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You need to remove the sender and check the part number. It might have the wrong sender.

Some of the 2 terminal VDO senders have a floating ground. They look like the sender for a gauge and a light but one terminal is for ground, not a light.
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Old 06-08-2021, 11:48 PM   #11
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Originally Posted by hiperfauto View Post
You need to remove the sender and check the part number. It might have the wrong sender.

Some of the 2 terminal VDO senders have a floating ground. They look like the sender for a gauge and a light but one terminal is for ground, not a light.
Couldn't you still check for ground engine off/on at W to see if it's for a warning light or ground input?

Although I wouldn't think a floating ground sending unit would be able to peg the gauge with only one connection

Last edited by James M; 06-09-2021 at 12:02 AM..
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Old 06-09-2021, 12:08 AM   #12
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OP says he can't read the letters on the terminals but the gauge sits at 0 connected one way and it pegs below 0 when switched to the other terminal.
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Old 06-09-2021, 12:35 AM   #13
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Quote:
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it's got the G and W terminals.
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the letter markings on the sender are hidden by the heater pipe.
Ah I see, I only read the flip, not the flop.

Id'e still expect (correct me if I'm wrong, working off the diagram never used one) that a floating ground sending unit wouldn't move the gauge at all without a ground hookup as it's just an open circuit without it.
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Old 06-09-2021, 01:03 AM   #14
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I think you're right but electricity will do weird things when it can't find a path to ground.

I think the sender may be faulty. It shouldn't be too hard to test with a DVOM.

Last edited by hiperfauto; 06-09-2021 at 11:08 AM..
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Old 06-09-2021, 07:17 AM   #15
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John, I still have the VDO gauge and sender I got from you. If you need them I will mail.

Quote:
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G should be to the gauge (sending unit portion) and W should be for the warning light (switch). I'm sure you could find a chart of resistance values vs pressure and check between G and ground, if its within spec its probably the gauge.
I did that with this one, used an air pressure regulator to apply pressure, measured resistance.
Not sure I still have it but it was easy to do.
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Old 06-09-2021, 07:53 AM   #16
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Mike, thanks but I don't think that was me, maybe Aaron? I'll check it with a meter, probably not today though is supposed to be rainy after work.
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Old 06-09-2021, 12:38 PM   #17
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I don't know if this helps but with a resistor and 12V you could fake the sensor to the gauge:
https://vdo-webshop.nl/en/pressure-s...590691262.html
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