'87 5KCSQ finally attacked by electrical gremlins:-

[Mike Del Tergo]

Shef,
assuming yor connections are good, I'd check output at the alternator and 
work back toward the battery.  Likely suspects, voltage reg, alt its self, 
and possibly infamous cable crimp.
You didn't mention what Master Cyl your replacing but the brake is very easy 
and the clutch not bad.  Get yourself a pressure bleeder though to save some 
time and need for a second set of hands/feet!
Mark @ Adirondack has a nice little unit for $44, well worth it for those 
who change their brake fluids even semi regularly.
Mike
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