Question about oil pressure sensor / switch

[MoPar~Man]

This pertains to the LA small block, but I imagine the same oil pressure switch concept applies to other engines.

When you have an oil light in the instrument cluster (not an oil guage), I imagine that the sending unit on the engine is just a switch? And when the engine isin't running, it should read closed (zero ohms) to the block?

 

[Big_John]

And when the engine isin't running, it should read closed (zero ohms) to the block?

It will read continuity to the block (or ground).

It's a pressure switch that opens when pressure applied and is normally closed when no pressure.

 

[MoPar~Man]

I'm still in the process of re-installing my engine/trans into my new stub and getting all the plumbing leak-free, wires connected, etc.

A few days ago I was running the engine, I had the parking brake on, the instrument panel brake light comes on and stays on while the engine is running, but I swear that the oil light also came on before the engine starts, but it's not doing that now. I'm getting 12 v on the wire going to the sensor. Take the wire off, I'm getting infinite resistance from the sensor contact to the block.

 

[Big_John]

I'm still in the process of re-installing my engine/trans into my new stub and getting all the plumbing leak-free, wires connected, etc.

A few days ago I was running the engine, I had the parking brake on, the instrument panel brake light comes on and stays on while the engine is running, but I swear that the oil light also came on before the engine starts, but it's not doing that now. I'm getting 12 v on the wire going to the sensor. Take the wire off, I'm getting infinite resistance from the sensor contact to the block.

The oil light should come on as you turn the ignition switch. You have zero oil pressure, giving the ground and there is power to the light. It goes off as soon as the engine fires and oil pressure comes up.

You are getting 12volts on the wire because you have continuity through the bulb filament. Take the bulb out and you won't have 12 volts.

If you are showing open or infinite resistance at the sender with no pressure, the sender is toast.

 

[MoPar~Man]

I was flipping around rock auto, checking a few different years for the 318 oil sender switch, I figure the threaded hole in the block is going to be the same for a lot of different years, I see this sender:

Looks like what I have, except it has 3 contacts instead of 1. How does this one work?

 

[halifaxhops]

That is also for a guage/light. I have the single wire if needed, $20 and the ride

 

[MoPar~Man]

I'm going to buy the 3-wire sender, I figure one of the wires is for the oil light, the other 2 are a piezo-resistive element that reacts to pressure. I'll build a circuit to get a signal out of that and I'll have an oil pressure reading, put a readout in the cabin somewhere.