Carpokes Porsche Forum

A bit of background, I think the low oil level light is of great use on our cars especially my race car. The function of the float level is a simple ground that feeds into the gauge cluster. I like that on my endurance race car I can monitor the oil level in case something has gone wrong and my brother nearly runs it out of oil...but I digress.

The oil level is just a float with a magnetic reed switch that grounds when the level goes down. It is simple and basic as a sender. What I don't know is once it goes into the cluster, how it works to remove flickering or to latch the light on if it does this.

I have wired in a level sensor to my 944 race car and it is a simple ground to an ignition powered warning light. The issue I have is that the light will flicker when I rev the car. I assume that the float is bouncing around. I have solved this with a simple inline delay timer that is adjustable. The way the delay switch works is that if at any time in the adjustable ON window (about 3 seconds right now but it is adjustable) the float switch goes open (off) the ON signal is reset and a it requires another 3 seconds of a closed/ON signal to turn the light on. This get rid of the flickering of the light.

The next issue I have is that the light turns on with ignition on and the oil level at the full mark on the dipstick but once I rev past about 2,000 rpm the light turns off. I'm thinking the following:
1. The windage of the crank spinning is moving the float or the oil level around causing the float to move and the switch to open and the light to turn off.
2. the dipstick level may not be right and I need to truth that it is full

Has anyone figured out how the light works in the schematics for the cluster or wired the factory level sender to a racecar with a simple dash warning light?
Below are schematics. Bulb 20 section C11 is the oil warning. going to the cluster on pin 15 (third from the left, section B14). The light is switched ignition power from weld point J19 on pin4 of the instrument cluster (section D14).
What I dont get is where "CONNECTION ADD. ELECTRIC" pin 12 goes to and how it feeds the light. From the schematics it looks like the light is fed form pin 5 of "CONNECTION ADD. ELECTRIC".
What am I missing?
Where do the "CONNECTION ADD. ELECTRIC" terminals 1 to 12 go?

Ignore the "CONNECTION ADD. ELECTRIC"j... the pins don't seem to be connected to anything outside the instrument cluster.

So, as you have determined, the 12 volt positive comes through weld point J19 after leaving the fuse block at pin B13. It is protected by a 7.5 amp fuse number 18.

In order to turn on the light, you need a ground, which is provided by the oil level sender (G45) through pin 8 on the dme connector (in the passenger footwell) which enters the cluster at pin A15.

Like I said before, ignore the "CONNECTION ADD. ELECTRIC" pins. They may be there for testing at the factory. If you were really curious, you might use an ohmmeter to look for continuity between pin A15 and some point on the cluster.

I should clarify, I’m looking to hook ip the level light in my race car with no stock gauges. This means I’m looking for the magic sauce between pin 12 and pin 5 of the cluster.
The below photo is from the owners manual so there is something going on as it is not just a direct connection. There is some logic in there that would be nice to duplicate or understand.

I went through the schematic, and there is no signal conditioning. The line pulls low, and the lights come on.

The signal path from the oil level sensor comes in to CONNECTION ADD. ELECTRIC pin 12, is routed back to pin 5, and on to lamp 20 (oil level warning) and through the blocking diode to the "!" lamp. There is a table to the left that shows "oil warning" on pin 5 and pin 12, indicating the jumper. That table could use a lot better explanation of what the rest of it is doing.

My limited experience with reed switches is that they have some hysteresis, once there is enough magnetic field to switch them on, the field must decrease some before it will open.

I thought they added a little circuit board to the cluster for this? It may not show on the schematic...?

Assuming the sender is working, you might use an Arduino or similar to replicate the function described in that factory description. I'm not sure how you could do too much more to create a real time warning light since the lever will inevitably go up and down as you drive, corner, rev, hit bumps, etc. Unless the sender itself has some way to cushion/filter all that out, seems like you need some big picture logic to 'decide' when to turn on the light. I could be wrong for sure but seem to recall they added a circuit board to the later clusters to do that.

Tom wrote: Tue Sep 16, 2025 8:18 am I thought they added a little circuit board to the cluster for this? It may not show on the schematic...?

Maybe they did. There is nothing on the schematic about it. I have an early car, so don't really know.

Edit: After reading the listed owner's manual entry (I should have earlier) I have to agree. There has to be a module somewhere that performs the listed function.

Sorry for the derail.

Going through some ebay pictures of the back of late clusters, I think I have identified where the module connects. There are pictures of a wiring harness with cut wires connecting to this location. The 88 schematic renumbered the pins to 1 to 8, with 5 having no connect. This would seem to match.

Tom wrote: Tue Sep 16, 2025 8:18 am I thought they added a little circuit board to the cluster for this? It may not show on the schematic...?

From the description in the manual this seems very likely. The input into that logic board is what I'm wondering about.

944er, The circuitry up to pins 5 and 12 is very simple so something else must be going on to achieve the logic described in the owners manual. I also don't think the numbering of Additional Electric is correct, if you look at the schematics they are not labeled sequentially.

Maybe Lutz can share some knowledge as he makes the replacements for the flex boards on the back of the clusters. I will reach out to him.

Tom wrote: Tue Sep 16, 2025 8:27 am Assuming the sender is working, you might use an Arduino or similar to replicate the function described in that factory description. I'm not sure how you could do too much more to create a real time warning light since the lever will inevitably go up and down as you drive, corner, rev, hit bumps, etc. Unless the sender itself has some way to cushion/filter all that out, seems like you need some big picture logic to 'decide' when to turn on the light. I could be wrong for sure but seem to recall they added a circuit board to the later clusters to do that.

I agree there needs to be some filtering and I did use a very simple delay timer PN T2L-ND-31-240U and this works well to remove the flickering. Now to get some logic on the float in operation.
I would love to have a little module like an Arduino but my skills, time and learning curve are not up tot the task.
https://www.automationdirect.com/adc/sh ... gKKbPD_BwE