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H4 bulb voltage feedback
CosKev3 - 11/4/15 at 10:45 PM

When I turn on my headlights(Dominators with H4 bulbs)my high beam warning light comes on dash.
I've measured voltage and it seems I've got circa 6 volts feeding back from dip beam into main beam power wire.
If I remove the relay for main beam I still get this circa 6 volts back into main beam supply when dip beam is switched on,so this means its bulb/headlight unit related?

Any ideas please?

Cheers

Dusty - 12/4/15 at 01:13 AM

The two filiaments share an earth within the bulb. Check you have wired up correctly. Then check the earth is electrically excellent both ends.

adithorp - 12/4/15 at 10:10 AM

Sounds like either your earth isn't good (check the chassis connection) or you've made a mistake with the terminal order. The earth is one of the side terminals (can't recall which) and it's common for people to assume it's middle terminal. Either way means the headlight back feeds through the main beam terminal.

http://www.easternbeaver.com/Main/H4_socket_wiring2.jpg

[Edited on 12/4/15 by adithorp]

CosKev3 - 12/4/15 at 01:26 PM

Thanks both of you

As you thought I had got the earth and main beam on opposite sides of the plug!

adithorp - 12/4/15 at 02:51 PM

quote:
Originally posted by CosKev3
Thanks both of you

As you thought I had got the earth and main beam on opposite sides of the plug!


Not the first, won't be the last.

I had a customer book his newly acquired Jag X-type in last week because every time he switched the dip beam on, it was "back feeding " to the dash main beam warning light but if he switched it to side lights, it went off and he wanted the "wiring fault" tracing... I switched it to dip beam with the stalk by pulling the switch "Oh I didn't know you could do that"

CosKev3 - 12/4/15 at 05:30 PM

'His' car? I could see a woman saying that but a bloke ffs!!!

Think I've realised where I went wrong, looking at the plug from the front rather than rear!