H4 headlight problem

hot66 · Post by **hot66** » Fri Jun 09, 2006 8:59 pm

Question for you electrical experts

I have just had some RHD H4's fitted. These were fitted by the person who has just been tidying up some paint for me so I didn't get the chance to see if the wiring was modified from the previous H1 set up..

Anyway, full beam is fine, a nice bright white light.

Dipped beam is crap. A dim orangy light. Can hardly see a thing. This can't be correct

The bulbs fitted are 55 / 60 watts.

I do have a volt meter, but I'm not that hot with electics.

What do I need to test for & is there anything obvious I need to be looking for?

Nick Moss · Post by **Nick Moss** » Fri Jun 09, 2006 9:04 pm

Sounds like a bad earth.

Barry · Post by **Barry** » Sat Jun 10, 2006 11:07 pm

That's curious: don't both beams share the same earth?

.

I'd start by pulling the lamp unit out, and putting the voltmeter (set to D.C. volts) from the earth terminal on the bulb holder to the dip beam power terminal (i.e. both the power and return on the actual bulb holder), and then same for main beam (obviously switching the appropriate beam on when testing). This tests the actual voltage across the bulbs: it should be the same for both main and dip, and just below the battery's voltage.

Then do the same going from the lamp's earth terminal to a known good earth, like the battery negative, if your meter's lead will reach (keep the meter switched to the DC volts setting, and the headlamps on).

When checking the earths, you shouldn't really see more than .3v max, anything over a volt indicates poor earth. I would suspect, however, that if the main beams are O.K., it's more likely to be a problem with the power side of the dip beam circuit: be very strange though: you're sure the mains are definitely giving full power?

If it's definitely not earth, then try headlamp wires, dip beam fuses, dip switch and make sure the bulbs are fitted correctly in their holders.

Barry · Post by **Barry** » Sat Jun 10, 2006 11:10 pm

Forgot to say, whatever the problem, it's more likely to be caused by the removal/refitting of the headlights themselves, rather than something further away, like the dip switch: this assumes that the lights were fine before

.

hot66 · Post by **hot66** » Sun Jun 11, 2006 8:12 am

thanks barry

I just need to work out how to use my multi-meter

Don't suppose you know which of teh 3 wires to the bulb is which?

Give me mechanical stuff any day

Lightweight_911 · Post by **Lightweight_911** » Sun Jun 11, 2006 10:25 am

Are you using the pilot lamp within the H4 headlamp for a sidelight ?

It sounds like the sidelight (pilot lamp) is the only bulb coming on in the dipped setting.

Similar symptoms can also occur when the main/dip column stalk switch has eroded terminals due to 'arcing' (sp?) - the timing of this fault could be coincidental.

hot66 · Post by **hot66** » Sun Jun 11, 2006 1:52 pm

Lightweight_911 wrote:Are you using the pilot lamp within the H4 headlamp for a sidelight ?

It sounds like the sidelight (pilot lamp) is the only bulb coming on in the dipped setting.

Similar symptoms can also occur when the main/dip column stalk switch has eroded terminals due to 'arcing' (sp?) - the timing of this fault could be coincidental.

I'll check. My initial thoughts was that they might have been wired up wrong when swapping from teh original H1's?

hot66 · Post by **hot66** » Sun Jun 11, 2006 5:18 pm

just checked.

Only one bulb, the main H4 one

Measured on V setting with dots underneath ( pretty sure this is Volts DC? ) on my multimeter

dipped beam:

yellow wire to brown wire .... 11.22
yellow wire to earth point .... 11.22

white wire to brown wire .... 4.86
white wire to earth point ....4.98

Full beam:

yellow wire to brown wire .... 10.16
yellow wire to earth point .... 10.25

white wire to brown wire .... 10.19
white wire to earth point ....10.29

have i done this correct & does any of it make sense?

Nick Moss · Post by **Nick Moss** » Sun Jun 11, 2006 5:23 pm

Not to me. Make sure you are getting a good earth by connecting the body of the lamp directly to the earth on the battery

Barry · Post by **Barry** » Sun Jun 11, 2006 5:36 pm

Yes, now I'm confused as well: certainly some odd voltages there.

Tell you what: following Nick's earth theory, if you've got some wire, put the headlights onto dip beam, then run a wire from the bulbholder's earth terminal (brown wire) direct to the battery negative. I.e. you are putting an additional (direct) earth onto the lighting circuit.

If the dip beam gets brighter when the extra earth goes on, it's an earth fault. If it stays the same, it's either the bulb, the position of the bulb, or the voltage coming into the lamp unit.

Some would say to set your meter to 'Ohms' (resistance) and simply put it from the bulb's earth to the battery negative: you should get the same reading as though you had connected the meter's leads together (0 ohms). The trouble with this method is that a modern meter takes almost no current to operate, so you could have one tiny strand of wire making a fairly poor connection, and yet the meter would read as though there is a good circuit there: hence the rather odd sounding tests in the initial post. These test the circuit under full load conditions which is usually better for our sort of thing.