Faulty bulb indicator on, but all lights are fine?

[rickjordan]

Lately on our '87 TD, when ever I turn on the lights, the faulty bulb light on the instrument panel illuminates. I checked all the lights and they are all working. Any ideas? It's real annoying driving around with a bright yellow indicator illuminating.

[JerryWagner]

check the license plate lights, this gets overlooked, isolate the systems, does it only come on when you turn on the lights, press the brake pedal, do the entire walk around with someone turning on the lights, some of the parking lights use 2 stage lights and if one stage is out it will look dim but still light up and make you think it's ok. let us know what you find

[jayb79]

Could be a bad connecton in the light socket or a bad ground. Pay close attention to the brightness of the bulbs or moisture in the lens. Do they all look the same(brightness)?
My TD had a burnt headlight connector that would sometimes give me a yellow dash light.

[rickjordan]

I'll check the plates and check for equal brightness on the parking lights. The fault light comes on as soon as I turn on the parking lights. So that elliminates the brakes and headlights.

[mototools]

Hello,
According to my owner's manual, the warning light will also illuminate if a bulb is of incorrect wattage (to low).

Rob

[carymcooper]

Rick:

I have had the faulty bulb light come on because the relay base pins were not making good contact with the plug sockets and another time when my headlight bulbs did not match exactly (different watts).

Cary.

[daddiojiggy]

you'll get the warning when you use the wrong bulb.be it low wattage or anyhting other than exact replacement.have you changed any bulbs lately?if so, start there.

[Since66]

I just recently had the same "concern". (Mercedes don't have "problems", lol) Turned out to be a rear, side marker light...the one around the corner from the brake light. It's easy to miss, since when checking I focused on the brake lights, running lights, turn signals, reverse, yada yada yada.

[G-Benz]

All posts are dead on...simply put, there are many possible scenarios that could set off the light.

I had the phantom light come on twice at different times and was able to eventually solve by inspecting the rear taillight housings.

Over time, the metal conductor rails (where the bulb sockets reside) get unseated and achieve partial (or no) ground. This is enough of a resistance difference to tell the bulb indicator that something is amiss (thus the light comes on).

Easiest test is to turn all of the lights on (engine running) remove the inside taillight covers, and inspect the bulbs. If any of them seem dim by comparison, press firmly against the rail near the affected bulb(s). If the light intensity changes when you do this, you have found your problem.

Generally, pressing down firmly on the rail will result in a "click", indicating that the rail is now reseated. Do this across the entire rail, as it may have been unseated in several places.

[rickjordan]

It was indeed one of the license plate lights. Thanks for the tip.