Smiths Oil Pressure Gauge

[garryc]

I removed this pressure gauge ten years ago at the start of the restoration and despite searching the web I can’t find a picture or a comment on the wiring from the oil pressure switch coming in. Does the other one whichever it is then go to the oil pressure warning light? I just can’t remember.

Thank you for your kind assistance.

 

[FridgeFreezer]

For a pressure gauge I'd assume one terminal is the supply (regulated or just 12v) and the other is the sensor (not switch), ground through the body of the gauge.

[Snagger]

It won’t be to the light.  The male terminal is probably the live feed from the fuse box, and the female for the earthing wire to the sender on a Tee piece where the oil warning light switch is located.  My logic on the guess of the terminals is just that the male terminal would permit a female on the live feed wire, which allows better insulation of the full 12v, nothing more, so is just a slightly educated guess.

[secondjeremy]

The sensor functions as a variable resistor - operated no-doubt by a diaphragm & spring or something - so the thing will earth through that.  It'll need an ignition-controlled supply - which can be taken from something convenient - its probably considered to be an extra and so relatively universal in fitting - and so uses a full 12 volt supply (as opposed to the 10 volt supply for the later fuel and temperature gauge) - but have a good look at the case to see if it says anything.

I'm sure the sensor side must be wired completely separately from the warning light.

The light is an entirely separate circuit which can be connected in parallel to the other panel lights.  (Possible query about overloading but I don't think that'll be a problem on an otherwise standard vehicle)

[Gazzar]

The light goes in the hole where your forefinger is. It's a bulb holder similar to the standard series unit.

[Snagger]

On 3/15/2020 at 4:12 PM, Gazzar said:

The light goes in the hole where your forefinger is. It's a bulb holder similar to the standard series unit.

That’s the gauge illumination light, not the pressure warning light.

[Gazzar]

Yep. I misunderstood the question regarding the light.

[Landrover17H]

To be honest, these things are variable at best. Think for a mo'...

1) You've calibration of sensor as one variable.

2) Calbration of gauge, another.

 

I'm all for tech when it works, however: If you can find a mechanical gauge, it'll be far more accurate. What you have will serve as a rough guide, but you won't beat a mechanical-gauge for accuracy.

Edited March 23, 2020 by Landrover17H

[FridgeFreezer]

2 hours ago, Landrover17H said:

I'm all for tech when it works, however: If you can find a mechanical gauge, it'll be far more accurate.

Unlikely, there's enough variables in a mechanical gauge too.

[Landrover17H]

Agreed, although I had it in the context of this thread, Smith gauges of Series Land rover vintage. Certainly anything automotive and with a Smiths name on it will be better as mechanical. Modern temperature sensors are better, however where it counts, flammable gases etc, mechanical gauges are law.