I have sussed my headlamp wiring as far as switching, but, if I wire a halogen h4(?) bulb with negative on the bulb with one of the other connections also wired, why do I get voltage out of the other connection?????????? this is done with the bulb wired direct to a battery....

It makes no sense when I have my switch gear so that dipped has no power when main is on!!!!!!!

Googled h4 bulb and dipped beam fillement stays on all the time, surley this goes against what people say about turning dipped off when main beam is activated????????

[Edited on 29/9/10 by dilley]

On an H4 you have one earth and 2 positive contacts each connected to the earth via one of the 2 filaments. As a result there is a circuit between the t positive terminals via the earth and if that terminal isn't earthed you will get current accross the other 2 terminals.
With a twin filament H4 bulb the dip shouldn't remain on when main is selected or the bulb (and lamp) will overheat and not last very long.


adrian

I will check again, negative to the middle post, positive to one of the others and im sure the non connected post has voltage!

What am i doing wrong?

Your connections are wrong. The middle connection is NOT negative (earth), the left hand one is Earth looking at the back of the bulb. That is why you are getting both filaments light up. Change the connections around and it will work correctly.

What he said ^^^

One of the side terminals is earth not the centre one.

Problem solved! thanks guys!