bulb warning light

[jammin1679]

Hello again, hope everyones well?
My problem is that the bulb warning light in my dash comes on when i switch the lights on, iv checked the lights and replaced the bulbs for the bright spark ones recomended to me, ( the problem was there before) and cleaned all the points, still it comes on with lights. any suggestions? im driveing a w126 300se on a j plate. Thanks!

[Dieselman]

Have you checked all the lights including the number plate ones.

[jammin1679]

Yep, all of them, the only bulb missing is the map light inside the car, could this be the problem?

[television]

I would think that you should use all original bulbs to get the circuit working correctly before you try the bright spark bulbs, a faulty brake lamp bulb will only show after using the brake pedal

[maddog]

are you sure you have fitted the correct bulbs , led bulbs for example will activate the bulb warning system

[R/T.E49]

Check they are all the correct wattage bulbs for lamps, as a 5w in a 10w will bring the light on.

[Parrot of Doom]

Dodgy connection somewhere I reckon, or bulbs not correctly seated.

[jammin1679]

after reading the posts iv just been and checked all the bulbs, wireing and wattage, all seems fine, the only one missing is the map light on the interior cluster, i dont think this could do it ?????

[Diesel Benz]

I don't think the map light should count for the warning.

It has been a long time since I've had a bulb warning (knock on wood), but if the warning comes when lights are switched on, doesn't it mean it should be one of the bulbs that are supposed to light up at that time? If all of those look like being OK, I would take a multimeter and measure the current for each bulb. May not be always easy to reach a connector.

It must be either too high or too low current, meaning a wrong bulb with too high wattage (it could read right on the bulb but still be wrong) or a bad connection somewhere or a too low wattage bulb causing causing too low current.

Even measuring the resistance from each bulb and verifying that pairs are equal would help (but does not give any definite answer).

[bolide]

The Bulb Failure unit works by comparing the current draw between the two sides of the car. If you remember your O-level physics it's a Wheatstone Bridge but, in this application, it also "knows" if the bulb rating is wrong on some circuits

The failure light come on when the two sides don't compare. If it lights up as you switch on the sidelights, you have a bad (or mismatched) sidelight or number plate light. If it lights up when the dip beam is switched on it's a bad dip bulb, and so on. From this you can easily determine where the fault lies

The final fault may be in the unit itself. Not that common, in my experience

The most common cause I've found is incorrect wattage rear sidelight bulbs. On W124 estates they should be 5 Watt on early cars and 10 Watt on later ones. I don't know when the change was made. I don't know what rating they should be for other cars

Nick Froome
www.w124.co.uk

[Diesel Benz]

The Bulb Failure unit works by comparing the current draw between the two sides of the car. If you remember your O-level physics it's a Wheatstone Bridge but, in this application, it also "knows" if the bulb rating is wrong on some circuits

This is how a Volvo used to work, 20 years ago at least. Don't know how a W123 worked and haven't been learning how my current cars work but the above sounds too simple. The car anyway is aware of both short and open circuits. If both rear park/drive lamps fail, the current would appear equal but the car should still be able to substitute this with another bulb (pwm modulating the intensity if necessary).

Should I read more or could someone confirm this with more details (latter would be preferable).

[jammin1679]

The bulbs in the headlights are H4. However when i orderd a new set i was told that i needed H1's, could someone set me straight please? Thanks for the above advice, i have a frend comming round to check the current, also have noticed that my left headlight responds faster than the right.