My handbrake light used to come on at random times , found it was coming on cos the level in the fluid reservoir was low due to the cluth slave clyinder leaking. Dunno if that could be anything related to yours
Like baby has already hinted at, I had the same on my 156 - fluid level low, this time due to a 'weep' at the connection between one of the pipes and a calliper. Used to flash going up steep hills (like 1:5 steep) too,
mine tends to do this in winter and after making sharp turns at speed.
turns at speed make me think its either the fluid level or the worn cables touching the discs. Its not the fluid level, not looked at cables yet.