Dipped Headlights Keep Failing?

[cexley]

I'm losing the plot with this one. The dipped headlights keep failing on my 7A Coupe Quattro 20V. I'm on my 3rd steering control stalk. Side lights, full beam, indicators - in fact everything works normally, but every 3-6 months I totally lose dip beam - and nothing else. I have had wiring checked and switches replaced and at a loss what the root cause of the problem is. Is it a relay (none shown in diag) or an earth issue?

The switches show no sign of damage, and I'm beginning to think I am replacing perfectly good column switches and some how curing or resetting somthing by dismantling it all and replacing the damn thing.

I hardly use the car at night, so nothing is burning out and no other services on the control column ever play up (washers, rear wipe, indictors, park lights etc etc). Just the damned dip beam every time. I spend my time driving around at night on the fog lights. Also, the dip beam has never failed whilst driving. It is somthing that stops when the lights are first put on. Give us a clue someone!

[mcandmar]

I would suspect a relay. Worth checking inside the headlight for the earth strap, its pushes onto a pin on the back of the lens. On mine they had corroded and caused the bulb to blow twice. Only noticed it as the wire was hot, gave it a wiggle and it snapped off. It wouldnt cause a total loss of dipped lights, i would expect thats something to do with the ignition key turning the relays on/off. I.e. when you remove the key you have parking lights and can flash the main beam but no dipped lights. Whatever relay does that isnt working is my guess..

[cexley]

Just went out for fiddle in the dark and the bizzare thing is the dips do come on when headights flashed. It looks like there is a seperate circuit for powering things in dip 'only' mode.

Thanks for the advice. I'll check out the wiring and the relays tomorrow and report back.

[newsh]

Pull the plug off where the loom connects to the stalk and look at the pins/sockets, has one of them been getting hot?

[cexley]

Took it apart, and sure enough the socket on the loom connection with the thick yellow wire connected (top right pin on block) was burnt out. Checked for current and it was still live. Cleaned up the connectors and reseated the connector block and all is working again. However, why did it burn out in the first place?

I suspect too higher watt blulbs have been fitted on dip beam. Not sure what correct fitment is for the 7A, but will check the bulbs. Mind you, if I have to drop the wattage on the bulbs, I'll need a white stick to drive on dip beam. Strangley, full beam is pretty good...

[mcandmar]

As above check the earth points, could be the cause of the overheating. The headlights on 7A's are actually quite good by Audi standards, there certainly way better than the projectors on the S2 and S4. Bulbs should be 55w H1 main beam, and 55w H4 for the dipped/main beam. (i.e. H4 is a dual element bulb).

Better bulbs help like the Philips or Osram Silverstar, they give a whiter light and are a little brighter. Also wiring them direct from battery through a relay with get more juice to the bulb. Other option is H4 HID bulbs but i've never tried them.

[newsh]

Took it apart, and sure enough the socket on the loom connection with the thick yellow wire connected (top right pin on block) was burnt out. Checked for current and it was still live. Cleaned up the connectors and reseated the connector block and all is working again. However, why did it burn out in the first place?

I suspect too higher watt blulbs have been fitted on dip beam. Not sure what correct fitment is for the 7A, but will check the bulbs. Mind you, if I have to drop the wattage on the bulbs, I'll need a white stick to drive on dip beam. Strangley, full beam is pretty good...

Do I win the cigar??
A little corrosion leads to a little resistance leads to a little heat and then its a vicious circle till the pin gets so hot it goes black and stops working, sometimes it will melt a hole in the plug If you make sure its clean and the contacts are making a good circuit then it should be fine. Try to close the female side of the contact up a little so you get some pressure on the pin. A little dab of silicon dielectic grease on the contacts will keep the moisture out, from Maplins or RS or you can use plumbers silicon grease from Wickes or B&Q plumbing section.

[newsh]

BTW I use Phillips Vision Plus bulbs, same wattage but about 50% more light.

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