Got me some of those small racing lights.

I know it doesn't matter which way round the two wires go into the small bulb, but what about the other three???

None of them have continuity with the metal casing of the bulb.

Pat...

[Edited on 11/8/07 by Avoneer]

Just found this:

Does it look right when looking at the back of the bulb?

Pat...
Rescued attachment hlight6.gif

Colours are wrong of course.

Pat ;-)

I guess one will be main feed, one will be dip feed and the third will be common.

I would connect 12V across 2 of the wires in turn.

When both filaments come on dull orange the unused one is the common. You then use the common and one of the others to determine which is the main and which is the dip, the dip being the filament which is off centre.

HTH

blick is earth,i,m sure white is main and dip id yella

I tried with a battery and am now blind - think I found main beam 1st when I was looking right into the light.

Will have another go when the white spot goes.

Pat...

It gets them every time

I've been fixing high-power studio camera flashes (amongst other things) for the last 6 years now and I still haven't learnt not to look at it when I test fire. You soon learn to use your peripheral vision until the spots go though

On the H4 bulb, there are two filamanets along the centre line, the top on having a shield around half of it.

Is one for dip and one for main, or do they both come on for main or what???

Pat...

Thinking about it, I think the shielded one is dip and the unshielded one main???

When I connect the yellow and white to a 9V battery, both filaments light up dull orange.

So is black earth?

With black on -ve terminal of battery and white connected, shielded filament lights.

With yellow connected, un-shielded filament lights.

Sound about right?

Pat...

He was so pleased to find Main Beam.

You should have seen his little eyes light up.



Sorry, I'll get my coat

Wasn't just my eyes - it was the whole garage!

Pat...

Now that you know black is earth, why not mount the lamp on something to hold it steady and point it at a wall. You should then be able to try each filament and see which is dip - sharp cut off - and which is main.