Strange Headlight Behaviour

[artscot79]

Well summats finally went wrong with the car and I'm puzzled.

When starting the car after its been left all night the headlights briefly flash on then instantly go off again all lights work fine no flickering all interior and rear lights are also fine battery voltage is low 9.3volts as the cars starting yet no battery fault engine running 14.4-14.5v im thinking the battery has had it but I've never had these symptoms with the headlights.

Open to any thoughts guys

[iantt]

Yep, seen it quite a few times. Nothing to unusual when battry voltage low.

[artscot79]

Figured as much can't moan its a 2006 on original battery so its done me well lol thanks for the reply

[artscot79]

Now the choices yausa Bosch etc etc sod it ford can do it I can't be bothered lol

[troy45]

If the headlamps are already switched on when you're trying to start the car then if the bulbs are say 60W or similar then you're pulling another 10A from the battery on top of the starter motor load, so if the battery is past it's best then could pull voltage down a lot more causing headlight control to drop out.

[artscot79]

No headlamps are off basically get in the car after its left over night turn it over the headlights briefly flash on if I was to switch I off and try again starts fine no flash of the headlights

[troy45]

Quick look at the wiring diagram, the headlamps are fed through relays in the GEM - these have constant 12V feed to relay coils then negative side goes through some canbus 'stuff' in the GEM then through hard wired headlamp switch to headlamp unit. Stalks feed to the GEM too.

The hard wired switches & headlamps don't really care if the battery is low or not but the GEM can very likely start acting odd when that's the case. Perhaps it usually holds the neg side of relays at high voltage but when voltage drops during starting it's enough for the relay to energise briefly. In comparison the tail lamps are just hard wired as they're always on whereas headlamps have canbus control for high beam, low beam and flash.

[artscot79]

Tail lamps don't do it so you may have hit the nail on the head there ill put a new battery in next week anyway as its pretty much passed it it did only start recently with the cold weather in only doing 10 miles to work then the car sits 12hrs then 10 miles back so all the short journeys will not be helping

[artscot79]

Spot on my friend gave the car a good run tho morning and tonight no flasing headlights called ford a trusted local who said he knew what it was.the battery in the car Is a 390cca battery however there are 2 batteries the 390 for basic fords but those with heated windscreens take a bigger battery 500+cca so that's the issue the battery isn't big enough to do the job.

As a bonus I got a discount so new battery to be fitted for £80