H4 Bulb Connectors

[GC8]

Can anyone tell me the function of each connecting lug on an H4 headlamp bulb, along with the readings that I should expect to see on a multimeter when everything is working as it should?

Thank you.

[Steve_D]

Looking at the pins on the back of the bulb.
Left vertical....Earth
across the top...Low beam
Right vertical....High beam

In terms of testing if you have continuity between each of the beam contacts and the earth contact then the filament is intact. Nothing more to test really.

Steve

[GC8]

Thanks Steve. By knowing which lug does what on the bulb I am better able to know what to expect when I test the wiring from the plug back. Im getting dim dip illumination in both filaments on one rising headlamp. Main beam and dipped beam work correctly on the other lamp and Ive ruled out the bulb; so it appears to be the spur to the pod thats at fault, but just to complicate it both sidelights have failed too.

[Pigeon]

Could be the earth has failed on that side. You may find that on the "working" light, the filament that's supposed to be off is in fact glowing a little... although the dazzle off the one that's on will make it hard to see. If the sidelight is on the same earth connection then it would explain that failing too.

[Steve_D]

Yep agree symptoms point to a bad earth.
If it's bad on one side then the other wont be far behind to best to either fix the earth or add an additional earth to both sides.

Steve