I have a 1990 740 GL with 300K plus miles on it. It has been really good to me but has a really annoying glitch that is driving me crazy. When I turn the head lamps on the "Lamp out" warning indicator on the warning light panel comes on. I have checked all of the lamps on the car and they are all functional. Any body seen this before??? What gives???

Thanks for the help.

Guy P.

Dear Guy,

Have you recently changed a light bulb?

Sometimes if you change one light bulb (ie a single headlamp) there will be large enough differences in resistance between the left and the right side light to cause the sensor to trip.

That being said you should check to see if all the lamps (ie headlights/signal lights/brake lights etc) are all matched. Second, since the sensor works on resistance, I would be inclined to clean the oxidation of all of your light contacts (espesically the head light sockets) since this oxidation could lead to a difference in resistance and = a tripped sensor.

After all this has been done, if the sensor still trips you may have a faulty sensor and a replacement may be in order. Just be warned that you want to make sure that the sensor has "bit the dust" before you buy another since you will be shelling out big bucks for a non returnable item.

Just FYI,

Tim

change to the "european" tail/brake light bulbs. I've done it on 2 different volvo's when all else failed and it solved it. The european bulbs apparently handle voltage differently than the us bulb stock numbers

There are plenty of 700's in junkyards now, and swapping the detector is a pretty simple job. Just remove the coin tray above the ashtray and pop out the sensor. It's a big red can in the front left of your fusebox. They do sometimes fail, though the most common problem I've seen is that the brake lights quit working. After changing both headlight bulbs (9004 halogens, if they're stock, by the way) so that you KNOW they're identical, I would try replacing the bulb-out sensor. Also check headlight ground wires for clean connections.
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Rob Bareiss, New London CT ::: 86 244DL, 87 244DL, 88 744GLE, 91 244: 808K total

Tim,

Thanks for the help. I'll give all of those a try.

Guy P.