A quick google search turned up this;

Federal Aviation Regulations

Home > Aviation Regulations > Parts Index > Part 125 > Sec. 125.205 -
Equipment requirements: Airplanes under IFR.Sec. 125.205 - Equipment
requirements: Airplanes under IFR.

No person may operate an airplane under IFR unless it has-

(a) A vertical speed indicator;

(b) A free-air temperature indicator;

(c) A heated pitot tube for each airspeed indicator;

(d) A power failure warning device or vacuum indicator to show the power
available for gyroscopic instruments from each power source;

(e) An alternate source of static pressure for the altimeter and the
airspeed and vertical speed indicators;

(f) At least two generators each of which is on a separate engine, or
which any combination of one-half of the total number are rated
sufficiently to supply the electrical loads of all required instruments
and equipment necessary for safe emergency operation of the airplane;
and

(g) Two independent sources of energy (with means of selecting either),
of which at least one is an engine-driven pump or generator, each of
which is able to drive all gyroscopic instruments and installed so that
failure of one instrument or source does not interfere with the energy
supply to the remaining instruments or the other energy source. For the
purposes of this paragraph, each engine-driven source of energy must be
on a different engine.

(h) For the purposes of paragraph (f) of this section, a continuous
inflight electrical load includes one that draws current continuously
during flight, such as radio equipment, electrically driven instruments,
and lights, but does not include occasional intermittent loads.

(i) An airspeed indicating system with heated pitot tube or equivalent
means for preventing malfunctioning due to icing.

(j) A sensitive altimeter.

(k) Instrument lights providing enough light to make each required
instrument, switch, or similar instrument easily readable and installed
so that the direct rays are shielded from the flight crewmembers' eyes
and that no objectionable reflections are visible to them. There must be
a means of controlling the intensity of illumination unless it is shown
that nondimming instrument lights are satisfactory.


Bruce
WWW.Glasair.org