Ignition light curious behaviour

[michael4]

Our car has Lumenition Magnetronic electronic ignition and an alternator. Everything works well (touch wood) but the ignition light behaves in an unusual way, to me at least.

Turn the key to start the car, light comes on, engine starts, light goes off. Everything normal.

But, turn the key to start the car, light comes on, engine starts, light goes off. Turn the key to stop the engine, engine stops. Turn the ket to start the engine again almost immediately and the ignition light does not come on. Engine still starts and no problems.

If I leave it a few minutes or alternatively disconnect and re connect the battery, normal correct service is resumed.

So why does the ignition light not come on if I go to restart the car within a few seconds of stopping it?

[myoldjalopy]

Its possible that in the past someone mixed up the oil and ignition lights at the back of the speedo so that there is still some residual oil pressure after switching off and turning back on immediately, causing the light not to come on when activating ignition. Leaving the engine off for longer, the oil pressure drops and 'normal service is resumed'. Try temporarily disconnecting the alternator and see if what seems to be the oil light does not go out on firing up......

[svenedin]

This sounds very likely. What appears to be the ignition light is actually wired to the oil pressure switch......

Although I have never taken an oil pressure switch apart I presume it has some kind of plunger and spring inside. It is a normally closed switch that opens the contacts when the oil pressure rises above a certain level. The opening of the contacts causes the path to earth to be broken and the light on the speedo goes out. Either through residual oil pressure or the mechanism inside the switch having a tendency to stick, the contacts are remaining open.

Stephen

[michael4]

Thanks, I will have a go and see how things work out.

[geoberni]

The above comments seem very likely.

Check the colours of the wiring going to the two lights, or even one of them, because if one of them is wrong, so must the other be...

Oil Pressure light = Green & Green/Yellow

Ign Light = White & Brown/Yellow

[michael4]

I've just had a look at this.

With the alternator disconnected and ignition on, the ignition light is on and the oil light is off

With the oil sender disconnected and ignition on, the oil light is on and the ignition light is off

With both disconnected both are off (obviously!)

So the excellent diagnosis is correct and I need to switch the lights in the back of the speedo

Thanks all!

[oliver90owner]

A simple initial error and a simple fix (there not really being much of a’fault’).

Maybe the OP should read through the saga of two recent threads by Wes, in the mechanical section.

Understanding the basics of these simple engines can be challenging for some new users. It is good that the issue has been resolved before a really urgent issue arises - like oil pressure failure - which could reduce the engine to scrap!