LED warning light glimmer

[Carboy0]

I have tried searching for an existing topic before posting, but can’t find one with this exact problem. I have replaced the various dashboard instrument and warning lights with LEDs and am generally pleased with the outcome. I have one niggle however; the oil pressure/brake warning light (triggered by the PDWA) was fine (off) with the old incandescent bulb, but now with the LED it is permanently glimmering, it’s hardly noticeable during the day, but at night it is v annoying, as the red light draws my eyes all the time.

So far I have 1. Checked the PDWA and the switch is centred. 2. I have fitted an oil pressure gauge and can say that there is plenty of pressure in all circumstances.

From this I think that the primary functions of the light are not the cause. I know that LEDs will glimmer with virtually no voltage, so I am wondering whether there is a residual power connection leaking through the light to earth, but I haven’t got a clue of where to look.

The car car is a LD20,000 plus Mk2, has anyone else noticed the same problem?

All help appreciated.

[StagJonno]

Bit of deja vu here, Chris. I replied to your post of yesterday, though I agree, it's better as a separate thread:

"Chris - can you give a bit more information.

1 - to confirm the wiring arrangement you've got - does your PWDA warning light come on with your H'Brake warning light?
2 - have you changed the PWDA warning light for an LED type as well as those in the warning cluster?
3 - Which warning light is glowing inappropriately?"

From the additional information you've posted today, it confirms the PWDA warning light being linked to the oil pressure warning as per the early wiring and also confirms the Oil warning as the inappropriately glowing warning light.

I can't see anything obvious from the Haynes wiring diagram, other than perhaps a bit of moisture or internal insulation breakdown within the oil pressure switch, or possibly moisture inside the warning cluster. As you say, LEDs can start to activate with pretty low voltages. If you've got a multimeter, you could check the voltages at the LED.

Good luck

Jonno

[Carboy0]

Sorry Jonno, I couldn’t find the topic that I had resurrected, thanks for posting again.

I have not replaced the bulbs in the warning light cluster yet, just the instrument panel ones. The light I am referring to is the red one in the top centre of the dashboard. I have just been out to take these pictures.

1. Ignition on and engine off, choke out.

2. Engine running , choke out.

[Carboy0]

Unfortunately, there is too much background light to see the big red light glimmering.

The handbrake light in the ‘cheese’ doesn’t come on at all (need to look into that separately), likewise the oil lite. From my reading, I understood the big red light should oil pressure and brakes, depending on condition, have I got it wrong?

[StagJonno]

OK - I understand better now. H_brake Brake Fail Warning Circuit Mods.pdf

Have a look at the attached pdf of a drawing of the early arrangement I harvested from here a while ago (together with a mod that can be done to make it even better than the later wiring). The whole arrangement is designed so that you get a bulb test of both the PWDA and oil pressure warnings when you first switch on the ignition. This arrangement needs for the resistance of both bulb filaments to be similar. If, with the engine running, the operation of the PWDA switch will cause the PWDA light to come on on its own. Low oil pressure would be indicated by both the PDWA and the Oil Press lights coming on.

In your arrangement, the LED PWDA will not pass enough current to allow the oil warning to glow as normal, which is why your oil pressure light isn't coming on when you turn the ignition on. However, the oil pressure circuit will be intact, otherwise the PWDA light wouldn't come on in this test condition. If you have a low oil pressure situation, only the PWDA light will show.

If it were me, I'd swap the PWDA light back to an incandescent. This will give you back your oil pressure warning light. It'll also remove your current irritation, though it won't give the answer to the mystery. You could always try fitting an LED to the Oil Press warning light in the cluster and see what result this gives - I wouldn't want to predict the outcome as I don't have any info on the internal configuration of the LEDs. I think they may be using some IC drivers rather than a simple resistance. Alternatively, if you want to go LED in the warning cluster, then I'd implement the modification shown in the attachment using a diode with a reverse voltage rating of 50V or more (to prevent transients causing a failure). For reference, the warning cluster you have seems correct for "from LD20001 onwards" (there are differences in some of the warning cluster bulb polarities between this and earlier cars).

Jonno

[DJT]

Put the original bulb back. Simples.

[Carboy0]

Thanks guys,

I was planning to switch to LEDs for the warning cluster as well, in the meantime I’ll switch back to the old incandescent bulb for the time being.