Greetings!

Last night the brake light (not the parking brake light) came on last night, but intermittently. It'd go out when I slowed down below about 5mph, and would come back on when I accelerated away. Today, my wife reports it just stays on. Any thoughts?

Barra

The red brake warning light on the cluster comes on when the fluid level is low. It is triggered by a float switch in the master cylinder reservior. Fix your leak and top up, and it will go off.

Do you mean the ABS light by any chance? If so, then you don't have too much to worry about. The sensors that run checks on the ABS system can wear out or destryed by dirt and so the computer doesn't receive the signal it should and thinks the system is malfunctioning.
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'Where's your common sense?' 'It left me when I was 5'

Unfortunately no, the brake warning light (not ABS). I had a look when I got home and found brake fluid on the inside of the left rear wheel. Further inspection showed the brake line to the caliper had worked slightly loose. I cleaned it up, tightened it, pumped the brakes, no fluid seepage. I'll top off with dot 4 tomorrow and just keep an eye on it.

Cheers!
Barra

PS. Forgot to add: The car has ABS and the brakes seem to work just fine.

I have never seen this on a Volvo but on some other cars I have seen a spring under the brake pedal give out. It is like a little spring loaded button that turns on the brake lights when you hit the pedal. It should be somewhat visable. But like I said, I'm not for sure how it is set up on a Volvo.

My bad...I wasn't quite clear. It's the Brake warning light in the dash that comes on.