Robert (bombero) - Scotland AO

Low Oil Pressure Warning Switch - Wiring Diagram

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My 2ltr Zetec has a low oil pressure switch but it's never been wired up (I'm currently running with a pressure gauge only). I want to fit a warning light in the dash and wire up the switch. Does anyone have a simple wiring diagram that they can post up for me to follow..? Cheers!

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I think its as simple as wiring one side of the light to the switch, and the other to a 12V supply. When the switch closes through lack of pressure it completes the circuit and lights up...

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12V feed from ignition switch (so the oil pressure switch circuit is only live while the ignition is on) to one side of the warning light, the other side to the oil pressure switch. When the oil pressure is low the switch completes the circuit to earth, light comes on. Simples.

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A little unclear still ..

The switch only has one terminal - I assume that this should be ignition live?

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Nope, like FBB said, the ignition live goes to one terminal on the oil pressure warning lamp. The other terminal, (the ground), then connects to the terminal on the OP sender, when there's sufficient oil pressure the switch in the sender is open and there's no light lit.

When the pressure drops below the senders trigger level, its internal switch closes and the current flows through the bulb, through the sender into the engine block and back via the blocks ground strap to the negative terminal on the battery.

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If you think about it the switch is really completing the -ve or ground side of the light - there's only one wire because the switch is grounded through the engine..so you have:

Switched 12V->Light +ve->Light -ve->switch->(engine)

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As far as i'm concerned the oil switch is a make to break switch. I mean when you turn on you ignition switch the oil light comes on, when you start your engine the light goes off as pressure has built up and broken the contact.

Agree that live feed to come off the ignition switch, if it did't you light would be on all the time.

Terry

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Would I be correct in thinking if the negative is attached to the OP switch sender and the +ive temporaily attached to the +ive side of the battery the light should come on

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44 minutes ago, S2T said:

Would I be correct in thinking if the negative is attached to the OP switch sender and the +ive temporaily attached to the +ive side of the battery the light should come on

Yes, thats correct, negative engine, positive from ignition/ battery  , basically joined by a light bulb.

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I would think most wiring looms already have a wire for the oil pressure sender ? - I think mine did but can't really remember - white & brown wire rings a bell but either way it's not difficult to run a new one up to the light.

As a thought on the standard oil pressure switch though - most come on (or go off) at about 8-10psi or 1/2-3/4bar - that's probably fine for a road car but I changed mine for a 20psi - 1.3bar as I wanted a bit more of a warning if things were going wrong (although I have a gauge which I watch avidly !). You can also get adjustable switches. On my old engine the 20psi switch used to come on at tickover on a hot day - a sign that the bearings / pump were on their way out (which they were) - new engine has much better pressure and is well above the 20psi at tickover.  

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Does this help?

oil.jpg

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that's nice :yes:

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1 hour ago, IanK said:

Does this help?

oil.jpg

Busy then ? :laugh:

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Also make sure the switch operates at something sensible.  A 6 psi warning is a bit late in my opinion.  I have my warning set to 21 psi.

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