The brake fluid warning light is on in park but when I let the handbrake off it goes out. the reservoir is full and the sensor has been rep[laced. If we shake the sensor unit new and old the light flickers.

daphne ellis, November 2014

"If we shake the sensor unit new and old the light flickers." - Would suggest to me the wiring close to the sensor unit, or crappy connectors at the sensor unit. You may get some insight by gently waggling indvidual wires (maybe carefully holding everything else still).
Intermittent faults like that are a sheer pain.
You may find its a common fault and mentioned in online fourms.

Gary, December 2014

Hi you probably have a wiring fault ..on a 23year old vehicle the fault could be anywhere

norb, December 2014

Its a Leyland Daf Roadrunner 1991

D ellis, November 2014