"Brake" Warning Light under Acceleration

[Lawrence C Leung]

Hello Listers:

My '89 200Q has been flashing the "Brake" warning light under moderate to
hard acceleration, such as entering traffic or passing. It doesn't seem
related to boost level (occurs anywhere from 0.7 - 1.3 bar on the factory
gauge) as at times where there is elevated boost, such as going up hill
without accelerating, the light doesn't come on. Is this a sign my
hydraulic pump is failing (my bomb is already pretty weak, so I imagine
most boost is coming entirely from the pump). Note, ABS works, power
steering seems fine, but I also do have a leaky rack. Any ideas? 

TIA!

LL - NY