Headlamps

JohnS · Post by **JohnS** » Mon Oct 22, 2007 6:07 pm

Am I right in thinking that when you go from dipped beam to main beam both bulb filaments come on?
JohnS 911T '73

Lightweight_911 · Post by **Lightweight_911** » Mon Oct 22, 2007 6:09 pm

No - I'm fairly certain the main beam filament lights up on its own.

JohnS · Post by **JohnS** » Mon Oct 22, 2007 6:25 pm

Thanks Andy. I think I have both on with main beam. Could this lead back to a faulty light switch? I have my suspicions - and the headlamp flasher does not work. JohnS

JohnS · Post by **JohnS** » Mon Oct 22, 2007 6:27 pm

Correction. Faulty headlamp main/dip/flash unit - not the on/off switch
JohnS

1972_911t · Post by **1972_911t** » Tue Oct 23, 2007 12:46 pm

Andy is correct two seperate filaments in the bulb only one on at a time, the switch is a possibility but it can also occur from the wires been on the wrong way.

Basically both filaments are connected to one common earth if you wire one filament as a live and the other as the earth when the live is powered it goes through the first filament to the earth which isnt actually earth so from there it must go through the second filament to get to the earth hench both filaments light. The other live must therfore be connected to the earth so when this is live it reverses the filament that is connected to the earth and light up only this one.

Hope that make sence

On H4 bulb it is clear to see what one should be the earth (the one attached to both filaments) the filament closest to the front is the high beam and the one further back is the dipped. Use a test lamp on the wires to confirm that only one wire is live at a time this will rule out your switch been the problem at the same time you can confrim which wire is for your high and dipped beams.

Steve

JohnS · Post by **JohnS** » Wed Oct 24, 2007 8:54 am

Thanks Steve. I will give that a try
JohnS

JohnS · Post by **JohnS** » Fri Oct 26, 2007 1:44 pm

Well, I've renewed the indicator/headlamp dim/main switch and for the first time the headlamp flasher works, so at least something was defective with the old switch.
Problem now is that on dip beam I'm getting 12 volts to the (yellow wire ) dip beam and 6 volts (white wire) to the main beam. When I put the main beam on I get 12 Volts to each!
Any thoughts on this one? MOT on tuesday!! Is it a defective light on/off switch?
Thanks
JohnS
'73 911 T

Barry · Post by **Barry** » Fri Oct 26, 2007 3:30 pm

I can't see that it would be the main light switch, as I don't think it can 'see' whether you are on main or dipped.

Tricky this, seems odd that the problem has remained (more or less) even after swapping the dip-switch over.

I suppose it can't hurt to go right back to basics: if you've not done it, just try switching the meter to DC Volts, and with the headlights on (either beam), put the positive to the earth at the bulb, and the negative to the battery negative. You should see almost no volts there (this represents the voltage drop through your earthing circuit.

If it shows a voltage, don't change anything, just put an extra wire on the bulb's earth, and run it direct to the battery negative. Re-check light operation.

What about the dipping relay (if you've got one): not sure how you would test it,but might be swappable, or by-passable (dodgy English, sorry), just to take that out of the picture.

If you've not done it yet, worth sorting out which wire does which inside of the boot, and unplugging the round rubber multi-plug in the boot, and direct wiring the main and dip from the bulb to the multiplug, with a direct earth. Disconnect the other plug altogether. If no change, then you know that it's not each bulb's wiring after it leaves the boot, the bulb holders or headlights, can't see how it could be the switch, and be odd to have two dip-switches produce the same results.

After that, it's got to be worth exposing as much of the front of the loom as possible (i.e. take any trim and carpet out of the way), and just make sure you've not got any clips or bodywork, or burnt insulation causing problems: highly unlikey, be this is a strange problem. It's a real offchance this, but might be worth going under the dash with a torch and mirror and just amke sure there's nothing that look as though it could give trouble.

Barry · Post by **Barry** » Fri Oct 26, 2007 3:31 pm

I'll grab the Haynes out of my car later, and have a look at the wiring diagram, see if there's anything else, or a better way of testing it

.

JohnS · Post by **JohnS** » Fri Oct 26, 2007 3:36 pm

Thanks Barry - I'll give it a try
JohnS

JohnS · Post by **JohnS** » Sat Oct 27, 2007 10:58 am

Another quirky thing about this wiring problem is that when I put a voltage meter on the plug at the headlamp bulb end it shows no power on dip or main if I use the a nearby earthing point. If, however, I use the earth lead within the headlamp bulb plug power arrives! Albeit 6 and 12 volt as explained earlier.
Any further thoughts?
Many thanks
JohnS

JohnS · Post by **JohnS** » Sun Oct 28, 2007 2:25 pm

Problem solved! Firstly the headlamp flasher/indicator switch was defective bit only in respect of the 'flasher' part. The real problem was the lousy headlamps on dimmed beam. I replaced the headlamp units and have some great buulbs from demon tweeks but still the problem continued. Now solved. It was the wiring into the bulb connector - the plastic bit that takes the 3 wires. Some where along the rebuild I had remove the 3 wires from the plastic bit and weeks/months? later put it back the wrong way. From the wiring diagram it looks like the brown earth wire goes in the middle (top) connector with the white and yellow wires to each side - this caised the problem. Close inspection of the plastic bit showed that I had scratched on the right wiring sequence. Brown to one side!!!!!!!!!
So if you see a red 911 with very bright headlights - its me!!!!
Thanks to everyone for their connemts and thoughts - as usual very helpful - especially when you begin to pull your hair out.
JohnS

Lightweight_911 · Post by **Lightweight_911** » Sun Oct 28, 2007 3:09 pm

Good news John !!

Just a note - if you've fitted uprated (higher wattage) headlamp bulbs, you might need to upgrade the relay(s) too.

Here's a link to a readily-available kit:

http://www.danielsternlighting.com/prod ... ducts.html

Jean Berk · Post by **Jean Berk** » Wed Nov 28, 2007 9:29 pm

I've done this mod - although I made my own kit from scratch. I also fitted 80/100w bulbs and they're loads better although still not quite as good as a modern unit, mostly due to poor-ish reflectors.
Well worth the effort.