Flickery headlights at idle

[Guest]

Sitting in traffic a few nights ago, I noticed from the relection of my headlights from the car sitting in front of me that my lights were flickering slightly. Later on, and another standstill, I saw the same thing. Slight revving made the beam stable during the rev, but once back to idle, they continued to flicker. I looked out for it again last night, and same thing. I also listened to the engine tone and it seems that it's not totally constant at idle (never has been) but varies just slightly, and that the subtle changes in tone accompanies the rate of the flicker of the lights.

Is this normal or is it a sign of something needing adjusting / fixing?

 

[Guest]

Hi John
Don't suppose it could be something loose, vibrating in sympathyat idle,lamp filament or reflector etc.Perhaps even a poor earthing point somewhere (if you think it is more likely an electrical fault).Just hazarding a guess.[]
Ian

 

[Guest]

The battery should smooth out these flickers, if it has a decent charge. This does sound a bit like the lights being supplied from the alternator, but this would show up on starting (ie low battery/poor starting).
Of course, the alternator is well hidden, so you can't check the wiring on that, but, as I said, I assume that it works, else the battery would run flat. Try the battery/headlight wiring (particularly the latter), to see if there is a loose connection.

 

[bones]

Funny I was talking to Mark about this last night and John B hits the nail on the head when he says it's probably down to a battery that isn't fully charged. My view is live with it because once installed a battery is always heading towards it's eventual demise and you'll notice this problem sooner rather than later. Best thing you can do is to clean and protect from damp all the relevant contacts.

 

[Guest]

Thanks guys, I'll check the wiring best I can (which isn't very well!) and look for any loose connections. The battery (Bosch, silver) was installed by the previous owner in June 2003. Loose connection(s) does sound like the most reasonable place to start looking, so thanks for that.

By the way, how long should I expect the battery to last before it's time for replacement? What are the typical symptoms of a battery approaching the end of its life - the obvious things like problems starting, etc., or would it just stop? Probably inanely silly questions but it's only since I bought this car that I've been motivated enough in getting my hands dirty with understanding mechanics and electrics of any car, so forgive my early stages of ignorance! []

 

[bones]

I have the same battery of about the same age John, a battery is knackered when it loses it's charge so often it becomes annoying. I find I can leave the battery for two weeks in the coldest part of the winter before it becomes a problem. I haven't had to recharge it yet.

 

[smitty893]

John,
What headlamp bulbs are you using?
Most cars headlamps will noticably brighten when you rev the engine from tickover.
Alternators don't provide normal running voltage(13ish volts) until they are spinning, which if your battery is on the way out will look worse. If on top of that you are using high output bulbs it will be even more noticable.
Cheers
Stephen

 

[Guest]

Bones, thanks for that info. I've not noticed anything to suggest the battery is on the way out yet, either.

Stephen, the bulbs are Silver Star (the brighter replacements to the standard H4 bulbs) and they've been in about 3 months without problem so far. The specific affect that I've noticed with engine at idle is that the lights flicker as you'd imagine a house bulb would flicker if there's a shorting in the wiring. My headlights flicker like that when the engine is idling (even after a good 1 hour driving). I'd understand if the light was stable but just changed intensity, and that's what I'd expect to happen with my lights, rather than this kind of 'shorting' effect.

A bit odd....

 

[smitty893]

John,
A further thought...I've read recently that the wiring is on about the limit for even ordinary H4 bulbs. If the connections are a bit dodgy this will put a further strain on the wiring.
Might be worth thinking about a relay to help matters...try the below link

http://members.rennlist.com/msucro1/relaykit.htm

I presume the idle speed is correct and the alternator belt is ok.
Cheers
Stephen

 

[bones]

If you read last month's PP this is the main topic in the SC Register article, since writing that two drivers of older model 911s confirmed that they were successfully using higher wattage bulbs. However nobody can feel the heat generated in the wires or the temperature at the headlight whilst driving, also if a fire destroyed a memebers car the insurance company would check all the electrical system and if non-standard parts were found to be a contributory factor the owner wouldn't get a payout, worse if 3rd parties were injured the owner could be sued. I can't therefore on the grounds of safety recommend fitting high wattage bulbs but if you do, add a relay it will make the system less marginal and guarantee 12 volts to the bulbs. You can of course use contemporary high performance bulbs of the legal 60-55 watt rating.

 

[smitty893]

Just to clarify - I wasn't recommending the use of higher wattage bulbs, just the relay to "relieve the pressure" on the existing wiring.
Cheers !!

 

[Guest]

The ones I fitted I bought from JZMachtech, high performace Osram H4 Silver Star 12v jobbies, rated at 60-55 watts, so I wouldn't have expected these to be the culprit.

 

[Guest]

Hi Stephen, just got round to reading the rennlist link in your post. I'm wondering if I should fit a relay for the headlamp circuit, after reading that and Bones' post. I get the impression that even with standard bulbs the circuit is marginal, which I didn't know.

So, 2 questions:

• is fitting a headlight relay really as easy as it sounds? (I've never done anything truly spannery yet!)
• following on from Bones' advice, would this be classed as a mod by the insurance company?

 

[bones]

John the relay fitting is easy if you can use a soldering iron, if you are near London and buy the kit pop over and I'll help you fit it. Tell you Insurance co. about any mod's you make , photograph what you've done and send it to them as a recorded delivery. Generally if you tell them about things they are ok, an SC s performance even when tuned is small beer next to some of the other performance cars they insure. With a mod' like a relay it's my guess it is viewed as an addition to safety rather than detrimental to it. You are effictively improving the performance of your wiring system but check, unless they really understand cars the chances are they won't even know what the hell you are talking about.

Just seen you are in Watford, give me a call if you go ahead or need more info.