Land Rover Repair: 95 disco, regulator problem, voltage regulator

Question
my 95 disco has been running roughly,like not hitting on all cylinders, tachometer is jumpy and sometimes drops down to '0' when engine is running, also the headlights dim and brighten like a voltage regulator problem.  any ideas?

Answer
Definitely electrical, my first thought was alternator.  The tach signal comes from the Alt. output. A bad ground on the engine could cause all of these, or it may be several separate issues.  Check the ground points first, as that's the easiest/cheapest to fix.  Then have the alternator tested if need be.