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What does this warning light indicate / 92 240

That light starting coming on in my '86 when stepping on the brake and right after replacing the left tail light. The brake lights work fine, although the new one looks slightly brighter. Is this from the module sensing the difference in resistance in the circuit between right and left? Should I swap in the bulb from the old left light to make the warning go away?
 
Sedans suffer from issues with the flexible circuit board and the bulb holders. Wagons have issues with the bulb holders. Aftermarket lamps and bulb holders make things even worse.

The relay measures the "balance" of the current from left to right. If one side has more/less current, the warning light comes on.

I have heard of issues with different brand bulbs on each side causing an issue. Or if a ground connection is poor on one side.

The lamp means, "I drive an old Volvo with never ending electrical issues"
 
ZVOLV said:
The lamp means, "I drive an old Volvo with never ending electrical issues"
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It comes on when I hit the brakes on the 91 wagon with the broken tailgate harness and resultant lack of the cyclops light.

But I have come to like it and look at it as part of the cars "character".

Maybe one day I'll fix it.
 
No one guessed the correct answer.

The correct answer is it's a critical warning, telling you to reach in behind the cluster, twist and remove that bulb. Then carefully walk outside and throw it as far as you can.

Then go about your life.

Dave
 
I don't think the 3rd brake lamp is included in the circuit. There isn't another "side" of the circuit to compare current with.
 
The module does detect the third brake light being out. So, if you fix the tailgate harnesses the light may start behaving itself. Or, like in my car it keeps coming on randomly even though you have cleaned connections and have the same bulb in each side of the car. All lights are working nomially.
 
I'm trying to get to the bottom of this on my car too. I've got it so now the light only comes on when I brake. Auto Zone said my brake lights are 7258 which is 26.9w and 7506 which is 21w, versus the 1157 21w and 1156 21w that the owners manual calls for. I'll get the 1157's tomorrow but I figured I would ask here before hand to get some more tips.
 
The old dual filament bulb designation was 1073 which is also still available. I use them for a bit less heat vs using the 1157 bulb. I just
noticed on my car today the left running light bulb is somewhat less bright than the right. So, when it stops raining I have some connections to clean.
 
OVERDRIVE said:
I'm trying to get to the bottom of this on my car too. I've got it so now the light only comes on when I brake. Auto Zone said my brake lights are 7258 which is 26.9w and 7506 which is 21w, versus the 1157 21w and 1156 21w that the owners manual calls for. I'll get the 1157's tomorrow but I figured I would ask here before hand to get some more tips.
Click to expand...

The important thing is just to have them matched in resistance/wattage left to right. The sensor is supposed to detect a difference in power draw across the two sides and light up when there's one present. It's a complex but fairly dumb part.

I would not go any higher in wattage than the factory specification as the taillight housings are known to melt when overheated. I have successfully run LEDs in the taillight housings which draw <5W without tripping the sensor, but I was careful to always install in pairs left/right to keep things matched. Likewise if you modify the circuit (for example I added more LED brake lights in the rear fog positions) the failure relay won't care as long as it still sees the same load on both sides.

Make sure you don't have any loose, damaged or corroded contacts on either side which are pulling extra power (and potentially melting your bulb housings with the resulting heat!)
 
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