Does this mean low brake fluid?

They turn off when I start rollin... and it's only been doing it since it turned cold outside.

 

Could be a vacuum switch.

 

Mine do that too. But the light will usually only go off if I tap the breaks again. I was thinking it does that cause my rear shoes are worn down and are over-extending but Im not sure. Ive been putting off messing with my breaks till I get the money for new rear hub bearings and locking nuts. Previous owners or mechanic was lazy and just took a chizzle and hammer to it to get it off...