Headlights fading/blowing, electrical prob?

[JUV]

Since we bought our 02 plate 1.2 back in September we've been noticing an odd thing in the evenings - whenever the car is manouevring at low speeds (ie parking) with the headlights on, the lights visibly fade a little when the car is idling, and brighten again when moving. Sometimes there's a noticeable change in the sound of the fan at the same time, as if the motor's slowing slightly then speeding up.

We've also had to change the headlight bulbs a little too regularly - passenger side in October, driver's side a few weeks back, and then passenger side again today. Admittedly I changed the passenger side originally and may have made a bit of a hash of it, being my first time, or of course it might have just been a bit of a duff bulb - but it still seems odd.

Can anyone cast any light? We've had various other idle/emissions problems with the car, so far needing a new catalytic converter, throttle body, thrust sensor and EGR valve, so nothing would surprise us at this point frankly.

[alexperkins]

Sounds like the alternator, or you need a new battery. Thats what causes voltage fade like what you are experiencing.

[JUV]

Thanks - my first thought was the battery, but it's still showing a dim green in the indicator thing - anyone know how accurate that is?

Could just the fading up and down be shortening the life of the bulbs, or is that likely to be coincidence/something else?

[alexperkins]

Ye. Itll wear the bulbs out faster if its going all over the place.

[JUV]

So does anyone have any advice on how to tell if it's the battery fading, or the alternator failing? We've spent a lot on this car already so don't want to waste £50 on a battery if the problem lies elsewhere - on the other hand we've seen too much of garages already.

How much is a new alternator likely to set us back? I've also heard mention of the voltage regulator, is that another possible culprit or would we know if that was blown?

[alexperkins]

You ideally need to get the battery tested. Put a multimeter across the battery terminals when its running, and 10 mins after its not running and note down what the voltage is.

Voltage regulator could also be causing this, but try the above test first and let me know what readings you get.

[JUV]

Thanks, will do (once I borrow a multimeter).

[Veedub9n]

Same thing happened to me. Is your interior light flickering on idle??

I got a new battery sorted it out, interior light doesnt flicker, the radio doesnt go off at low revs when you turn the wheel and headlights dont flicker/dim at low revs.

[pip_polo]

my headlights used to dim a little when stationary/1mph turning the wheel. but not noticed it since i got the HIDs.

[JUV]

I wouldn't say the interior light flickered exactly - it's not quickly on and off - but I guess it does fade a little like the headlights on idle.

Anyone know the best sort of battery for a 1.2 S with aircon and the other electrical modcons? Do we need a "heavy duty" battery, or will the most basic cheap battery do the job? Sorry for all the really basic questions. I put our reg into the Halfords website and it suggested four batteries from £59.99 (for a "standard" 360 Amps/41AH) to a slightly massive £82.99 (500a/60AH), with a couple in between.

[Veedub9n]

Halfords were a rip off for batteries when i checked. I got mine brand ew for £50 at National tyres. Its slightly more powerful battery than the standard one aswel.

[RUM4MO]

I wouldn't say the interior light flickered exactly - it's not quickly on and off - but I guess it does fade a little like the headlights on idle.

Anyone know the best sort of battery for a 1.2 S with aircon and the other electrical modcons? Do we need a "heavy duty" battery, or will the most basic cheap battery do the job? Sorry for all the really basic questions. I put our reg into the Halfords website and it suggested four batteries from £59.99 (for a "standard" 360 Amps/41AH) to a slightly massive £82.99 (500a/60AH), with a couple in between.

The size of the battery you fit if this battery is duff, could be determined by the sort of use you put the car to. In this cold weather if you jump in start it and whack on the heated rear window + lights + heater fan, then do a lot of stop-go driving mainly stationary at hold-ups and lights, then the battery will end up getting run down quite a bit - that is when a bigger and newer battery would be good - but not as good as frequent longish high speed runs. One other problem could be a broken excitation lead to the alternator that stops it charging at low revs (I believe) - there is a cable joining plug/socket under the car carrying this excitation lead - and it is exposed to corrosion etc - this tends to be more of an issue with TDI engines maybe due to vibration and engine movements. The voltage regulator will be built into the alternator to keep things compact. Other thing might be that with the frequent stripping down of your car, an engine earth might be missing or partially or completely fractured. You can buy a cheap multimeter in Maplin - just remember not to get too adventurous with it if you buy a cheap one as it will have a very low input impedance - so keep away from ECUs etc! - but is perfectly okay for checking battery voltage.

My mother-in-law has a 9 year old Fiesta on its original battery and she drives it half a mile twice every other day - it was quite happy with this until the recent cold weather came - and it suddenly said "no more"! Even my wife knows that cars are not made to survive this sort of treatment (I've trained her well!).

[JUV]

Great, thanks for all the advice. Will try a decent new battery (from somewhere cheaper than Halfords) and see where we go from there - certainly the existing one looks to be down on its charge (dark green indicator) so a replacement isn't going to hurt.

Good to know the alternator and voltage regulator are one in the same too - takes some of the uncertainty out of things, even if it does inevitably put the price of a new one up. Thanks again.

[sylvester]

Remember not to touch the headlight bulb glass when fitting them, if the connectors aren't a tight fit this can cause premature bulb failure along with overcharging, usually you would find all the bulbs would fail if overcharging was the cause.

[tim80bwi]

Have this same issue. Doesn't really bother me much so never thought anything of it. My guess would be battery though.