Panel lights

[spyzee]

A few months back as I was stretching the last panel light to push it into the rev counter I suddenly lost all panel illumination. I've tried various things as I don't want to get the dash out again but nothing has worked until today. I pushed a large pin down into the live wire side of the bulb holder and attached a wire to the pin and then put a current through it. All the other panel lights immediately lit up with the exception of the rev counter bulb.

So I have a few questions which I hope someone can answer:
Why does it do this?
Are the bulbs in series like the old christmas tree lights?
Is it the bulb or the bulbholder that is broken?
If it is the bulbholder does anyone have a spare I could buy?

many thanks,
Colin

[paddy]

The lights are all wired in parallel.

It sounds to me like one or more of the instruments isn't earthed properly. This can have the effect of routing current in series through the bulbs because the earth of one is connected to the earth of another, but not to earth itself. Check that and you should get three out of the four bulbs working.

I think you'll have to post a photo of the bulb holder just to make sure we're talking about the right one. I have a few spares that might fit.

Paddy

[spyzee]

Hi Paddy,

I don't understand the earthing bit. The bulbs are in plastic holders with one redwire going in and one black wire coming out. If, on the loose rev counter bulbholder, I put a pin in the black wire and earth the pin, nothing happens. If I put a pin in the red wire and pass a current through it then all the bulbs light up except for the rev counter one.

[paddy]

Maybe my last comment was a red herring But I did have a similar situation on mine where a poor earth for one of the instruments gave similar odd problems.

I'm looking at the Plus2S wiring diagram now. They are all wired in parallel. The red sides should all get power from a read and white wire from the panel switch and the black sides should all be connected to one another. It looks like all but one of them is connected directly to an earch, but there is one light (I assume the one for the rev counter itself) that is earthed separately; there is an additional black earth wire to the rev counter which looks like it acts as the earth for the rev counter itself, and then this in turn is the earth for the final light. There are two black earth wires to the rev counter. (You need to look at the diagram I think, it's too hard to put into words.)

It's hard to see how you get your symptoms with only one failed connection. But if the black wire that earths the rev counter is not connected then you can see that you could have a situation where all but one of the lights comes on.

In any event, when the panel switch light is on, you should be able to measure 12v at the red wire (measured relative to a true earth). Try to resolve that part first, because that aspect of the wiring, confusingly, is simpler than the earth part. Then check that both of the black wires to the rev counter are connected.

Good luck

Paddy

[spyzee]

I'll give that a go in the morning and see what happens.

many thanks,
Colin.