Was wondering were the bulb failure sensor is on an S90. Brake lights come on once in a great while but not very often. I want to try Marks suggestion of checking for a bad solder connection but I don't know where it is. Tim told me to look by the rear tail light but there is nothing there. I suspect its behind the ashtray but not sure. Anyone know? Thanks. KM

the bulb failure sensor appears to be contained within the Lamp Control unit located in the trunk, under the driver's side floor panel. Were you able to locate/replace this component? Did it solve your problem? I am experiencing the same issue.

Looking at the sketch in my Volvo Service Manual Wiring Diagrams for 960/
S90/V90 1997-1998,

The sensor looks to be near the power antenna motor and a fuel inlet pipe.

Left rear fender, back from the wheel well. You will neeed to remove the carpet and vertical panels to get at it.

Picture shows a square thing aound the size of a cigarette pack. It has one connector with a gang of wires to it.

Power from the brake light switch comes in a Yellow-Brown wire, which is probably inside a harness. It connects to terminal #10. Check that there is 12 volts present to either clear or indict the brake light switch.

Good Luck,

Bob

:>)

I'm pretty sure it's in the same location as it is in the 940's. Behind the ashtray and to the rear of the fuse block. If it is similar to the 940s, you will also lose cruise control. It's simple to replace and I got a new one for a 940 for about $53 delivered. Took 5 minutes to replace.
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94 940 112K ,98 V90 147K