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low pressure oil switch - stopped working

Started by _Agent 34_ , Jan 06 2019 06:19 PM

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8 replies to this topic

#1 _Agent 34_

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Posted 06 January 2019 - 06:19 PM

hi all,

bought a low pressure switch and it was working and sending a signal to the bulb, now the bulb is not showing the oil pressure is low.

the switch has three electrical outlets on the back of it.

one is earth the other is to the circuit which makes the light come on.

its set at 35 psi

it's not coming on and need some advice on how to test if it is the LED light or the switch

thanks

G

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#2 Bigfella237

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Posted 06 January 2019 - 08:54 PM

So what's the third terminal for?

If you're sure there's no (positive) power involved you can simply ground the wire, bypassing the switch altogether, and the light should be on whenever the ignition is?

If the light comes on then it has to be the switch (assuming the switch is earthed to the block); or if the light doesn't come on then the problem is further back in the circuit (I'd suggest replacing the bulb to start with).

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#3 RallyRed

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Posted 07 January 2019 - 12:15 AM

Hi Grant. what is the brand/part number of the switch?
The factory set up just earths/grounds the single wire that comes from the globe.( as noted above).
The new switch may be different configuration, it prob. has the ability to act as the orig. , but if you can advise the brand/ model/ part number, we can be sure.

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#4 _Agent 34_

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Posted 07 January 2019 - 06:10 AM

Hi col here is the part = it's an adjustible switch http://www.gauge-sho...e-switches-nonc

I just don't know how to test the switch.

the switch will activate a light if the oil pressure is less than 25 psi and once the pressure get higher then the light goes off

yes there is currently two wires going to the switch and im pretty sure that they went back the same way.

The only other issue is that the LED light is burnt out and rather than pull the instrument cluster out, i needed some advice on testing.

question 1- if i test the wire from the instrument panel to the switch with a test lamp should this light up the bulb

question 2- if the wires that went on the back of the switch from the instrument panel and the earth chassis = if these were reversed it should still give the same outcome ? Y/N

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#5 RallyRed

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Posted 07 January 2019 - 08:00 AM

That switch appears to be a generic single pole, double throw type switch.
In other words it has a -
a Common terminal
a normally open terminal
a normally closed terminal.
You want to connect your wires to the
Common and Normally closed terminals.
Thus the switch will pass current when power is applied. The light will illuminate.
When the engine oil pressure rises above the pre set value, the normally closed contact, will Open. The light goes out.
Likewise, if the pressure drops, the normally closed contact will again close.
The light will come back on.

In most cases, as you can see from the above, the normally open terminal, is not used.

All this assumes that you only have the one device connected to it. i.e it is wired like factory.
You will prob. find that one of your wires is just an earth/ ground. This is just because the switch you have is different to factory and doesnt have the ability to ground itself.
No dramas there.
If you think your LED is buggered, best to sort that out first.i.e replace it

Edited by RallyRed, 07 January 2019 - 08:01 AM.

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#6 _Agent 34_

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Posted 07 January 2019 - 01:05 PM

Ran a power source from one side of the switch and then used the test lamp through to earth on the other tab to see if there was circuit across the gauge and there was no circuit across the switch which must mean the switch is faulty and not reading.

engine was not running means no oil pressure and hence the contacts should be closed and then the current can go across.

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#7 RallyRed

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Posted 07 January 2019 - 01:58 PM

you need to be sure you tested from the "common" or "input" terminal ( see drawing) to the normally closed terminal ( top right in drawing).
I.e there are 3 terminals, you need to test the correct ones to get a normally closed circuit when it is laying on the bench.
As you can see, when you do get oil pressure, the contact swings across like a gate and connects the input side to the bottom right terminal.
When you loose oil pressure, it swings back and connects the input to the top right terminal.