Instrument Panel External Light Burnt-out stays on

300E 1989

Problem: The Indicator light for “External Light Bulb Burnt-out” stays on.
Action Taken: Checked all the external light bulbs and they are okay.
Are there any ideas why this instrument panel indicator light would stay on?

[300EE320]

Did you remember to check your 3rd brakelight as well? I overlooked that one and sure enough - that was my problem...

[J.HIDALGO]

Also check the tag's light bulbs.

[jcyuhn]

The third brakelight is a big culprit here. There are several light bulbs inside and it's virtually impossible to tell when only one of them is burned out - but your car know! Try disassembling the third brake light and checking the individual bulbs. Instructions should be in the owners manual.

[yhliem]

did you convert to european headlights? if so, that is why.

[JCE]

did you convert to european headlights? if so, that is why.

The conversion didn't cause any problems on my 300E with stock '+50' Philips 55watt H4 bulbs. What would be the source of the problem, (except maybe using an overwattage bulb as the STAR article discusses)?

[jsmith]

when it stays on, i believe it means either brakes or turn signal lamps. if it switches off with the light switch then it is something else.

[400E]

Don,
When exactly does the idiot light come on? Right on start-up? Or later?

The thing about the system that's not in the manual is that the idiot light only comes on when the circuit with the bad bulb is energized, and not before.

What I'd recommend is to start the car and keep your foot off the brake. Is the idiot light on? If so, there's something wrong with the warning circuit itself. If not, then hit the brakes. If idiot light comes on then, look carefully at the brake lights. If not, turn on the headlights to the first click. If idiot light comes on, look for a bad bulb in the running lights, license plate lights, etc. And so on.

I've had a time tracking down a bad running light on the SIDE of the rear light panel. Just work through it logically and you'll figure it out.

[J.HIDALGO]

I do not know if they are in the circuit but what about reverse or back up lights?????????????

[jsmith]

"when the bad bulb is energized"

i wondered about this because when the colder weather set in, i started to get the check light intermittently. it would stay on meaning brakes or turn signal. i've seen it go on by itself after hitting some small bumps. the manual is specific about what the lights are if the idiot light stays on but nothing about being energized as noted. given what i've observed in my car - i am now wondering if there are shorts in the warning circuit.

[JCE]

i've seen it go on by itself after hitting some small bumps.

It could be the short in the circuit you mention, but start by completely eliminating the easiest choices first. Check all the fuses in the fuse box - the older metal oxidizes and develops hairline cracks that can cause the fuse to work intermittently. Check ALL the bulbs in their sockets to make sure they have good connection, good filaments, and clean contacts (use care in removing bulbs - one of the forum members got a finger full of glass when installing a bulb). A loose bulb, dirty contact, or a marginal filament can cause a work/fail pattern.

Really hope that it isn't an electrical short - my flickering/failing right brake light was eventually traced to an exposed section of cigarette lighter power wire! It can take a fair amount of time to find and fix, as it could be on a seemingly distantly related circuit or a ground connection wire!

Good luck.