problems getting oil pressure light working

[evanmc]

1985 110 2.5NA

Problems that are probably my fault.

The oil plug on the sump came off, resulting in me leaving a trail, making it very clear whose house has the leaky vehicle.  I probably didn't torque the plug properly, so I did install a replacement and double checked the torque. I have attached a pic for your amusement. 

While I was spewing oil everywhere, I never saw the oil pressure warning light illuminate, and now I realize that I had been ignoring the fact that it was not illuminated when I turned the ignition on, so now I want to get thins to work.  I am certainly not well versed in troubleshooting electrics, but clearly I am missing something.  

The oil pressure switch has no continuity, but is normally open, right?  (A replacement did have continuity...)

But, the single wire that was hooked to the sender actually had power on it -- it's just supposed to be a ground. correct? Perhaps it was just mis-wired when I got it?

 

Thanks,

-Evan-

[steve b]

Ooops , most of us have had an oil moment at some point . 

The switch goes to ground below around 5 psi , so 12v on the white/brown wire with ignition on is good , touch it to earth to check the light works . 

It sounds like the old switch was not working if the new one has continuity from the terminal to the outer case .

One of my more stupid oil moments was not putting the drain plug in and then trying really hard to fill to level on my Trans-am 455 absolutely years ago , boy did I feel stupid .........

cheers

Steve b

[Tanuki]

38 minutes ago, steve b said:

One of my more stupid oil moments was not putting the drain plug in and then trying really hard to fill to level on my Trans-am 455 absolutely years ago , boy did I feel stupid .....

My "silly" moment was refillig the sump and starting the engine, not seeing oil-pressure, then noticing the new oil-filter sitting in the footwell...

 

The pressure-switch - yes, in the absence of pressure it connects the single wire to ground, so there's a current-path from the battery through the bulb - which lights to tell you there's a problem.

 

Fit a new switch - they're cheap to buy and easy to install.

[evanmc]

OK thanks, I did install the new switch, but things still aren't quite working.

I see 3.7V on the white/brown wire leading to the pressure switch -- that doesn't seem right.  I still have a bit more investigation here, it looks like.

Yes, and now I have a bit of mess on my drive to deal with tried several methods (dawn, simple green, something called oil eater, a blowtorch on the bricks) and nothing is completely effective.

 

[Mo Murphy]

The neighbours are all going to gang up on you 🤣

Mo

[Peaklander]

The warning light has +12v ignition controlled connected at one side of it and the other side goes to 0v through the pressure switch normally closed contact and the light is on.
When the pressure rises, the switch opens and the warning light goes out.
With the wire disconnected at the switch, you are measuring some volts because your test meter is acting like the switch and providing a path to earth for a very small amount of current (and it only needs this small amount to display a voltage).

It isn’t enough to light the warning lamp though. If it did, the lamp would drop all the 12 volts and you wouldn’t measure anything. So just connect the wire, check that the lamp is on with the ignition and then start-up and it will go out. 

[Peaklander]

If the 3.7V is there with the switch connected then you might have a bad earth and that might be at the switch thread. If you used PTFE on the threads it could be too thick. 

[FridgeFreezer]

^ What Peaklander said.

Also, you can test the light by connecting the switch wire to ground - the light should come on.

[evanmc]

And indeed, when I connect the white/brown wire directly to ground, the light illuminates, However, now I have no continuity through the switch that had continuity when I tested prior to installation. Argh.  No, no ptfe tape on the threads..

[Peaklander]

Only one of three things might have gone wrong then. You haven't pushed the spade onto the switch (very very unlikely) or you have a duff switch (also seems unlikely as you tested it for continuity before fitting).

The third is that you have no continuity between the body of the switch and the negative (0volts) at the battery. Is your engine block earthed? Can you use your multimeter to measure the Ohms between the body of the switch and the engine block and then the engine to the battery 0V? They should be zero or very low.

[steve b]

13 minutes ago, evanmc said:

And indeed, when I connect the white/brown wire directly to ground, the light illuminates, However, now I have no continuity through the switch that had continuity when I tested prior to installation. Argh.  No, no ptfe tape on the threads..

Take it out and check continuity again and while it's out crank it one or two turns with engine stop wire disconnected so it doesn't start , drip tray underneath . This is to check the oil is able to flow to the switch and there isn't a plug of oil sludge in there . 

As peaklander has said check the engine earth points are in place and maybe put a temporary small earth from engine to battery -ve  , that said I assume you just earthed the wire to the engine to check the light function so again earth issues seem unlikely ?

Steve b

[evanmc]

Perhaps it is just a bum switch -- as it failed the same continuity test out of the vehicle it passed before installation. Probably, maybe. Block is definitely earthed.

[evanmc]

9 minutes ago, steve b said:

Take it out and check continuity again and while it's out crank it one or two turns with engine stop wire disconnected so it doesn't start , drip tray underneath . This is to check the oil is able to flow to the switch and there isn't a plug of oil sludge in there . 

As peaklander has said check the engine earth points are in place and maybe put a temporary small earth from engine to battery -ve  , that said I assume you just earthed the wire to the engine to check the light function so again earth issues seem unlikely ?

Steve b

I will try to turn the engine over a bit when my oil order gets here.  in my test where I bypassed the switch and the bulb did illuminate, I ran a wire directly to the negative post of the battery.

[Peaklander]

Ah - so check continuity between block and battery -ve post using that piece of wire to get you all the way there. 

[FridgeFreezer]

Within reason almost any oil pressure switch that will screw into the hole will work - they all do basically the same thing, they all come on at dangerously low PSI, there's a few that work the "opposite" way round but aside from that it's a very simple thing.

[Peaklander]

14 hours ago, evanmc said:

 Block is definitely earthed.

I know that you said this ^^^ but then you said this:

 

14 hours ago, evanmc said:

...in my test where I bypassed the switch and the bulb did illuminate, I ran a wire directly to the negative post of the battery.

 

and you also said this

14 hours ago, evanmc said:

Perhaps it is just a bum switch -- as it failed the same continuity test out of the vehicle it passed before installation.

 

I suggest these steps:

1. Check the switch off the vehicle, for continuity from the terminal to the case, showing that it is working with no oil pressure

2. Check the block for continuity to the battery -ve. using that long piece of wire you used to confirm that the dash warning lamp works.

3. Then screw the pressure switch into the block and repeat the continuity test with that same wire, this time between the switch terminal and the battery -ve

4. Finally plug in the wire to the sender and turn on the IGN and the warning light should come on.

You don't need any oil or to crank the engine, to at least get this far.

[evanmc]

It ended up being a bum switch.  With a  second new one, things work as expected.

Now if I could just get rid of those oil stains on the bricks and the trail leading to my house on the street...

-Evan-

[Peaklander]

Good to hear that a new switch has fixed the problem. The oil stains will be harder to deal with.

[FridgeFreezer]

10 hours ago, evanmc said:

Now if I could just get rid of those oil stains on the bricks and the trail leading to my house on the street...

A gallon of brake cleaner, followed by a scrub with dish soap + water might shift the worst of it... some stuff will just hole onto it forever though.