I believe this should cover just about all of the necessary parts for all types of internal combustion and electric locomotives:

Both internal combustion and electric:

For all electric and internal combustion locomotives:

RADIATOR

COMPRESSOR (For the brakes and horn/air whistle)

MICROPROCESSOR_#

FRAME_JACKSHAFT_CRANK_SIDE_#

FRAME_JACKSHAFT_ROD_SIDE

BOGEY_FRONT_JACKSHAFT_CRANK_SIDE_#

BOGEY_FRONT_JACKSHAFT_ROD_SIDE

BOGEY_REAR_JACKSHAFT_CRANK_SIDE_#

BOGEY_REAR_JACKSHAFT_ROD_SIDE

For both AC and DC electric traction locomotives:

RECTIFIER_SILICON

DYNAMIC_BRAKE_GRID

For DC traction locomotives:

GENERATOR_# (for older internal combustion locomotives until about 1975 that did not use an alternator/rectifier combination, and for motor-generator electrics)

FRAME_WHEEL_#_TRACTION_MOTOR_DC (DC and AC traction motors have distinct differences in construction and performance)

BOGEY_FRONT_WHEEL_#_TRACTION_MOTOR_DC

BOGEY_REAR_WHEEL_#_TRACTION_MOTOR_DC

For AC traction locomotives:

(AC traction locomotives have either one inverter per truck or one inverter per axle, and are a major reason for the significantly higher cost compared to DC traction locomotives)

BOGEY_FRONT_INVERTER

BOGEY_REAR_INVERTER

FRAME_WHEEL_#_INVERTER

BOGEY_FRONT_WHEEL_#_INVERTER

BOGEY_REAR_WHEEL_#_INVERTER

FRAME_WHEEL_#_TRACTION_MOTOR_INDUCTION

BOGEY_FRONT_WHEEL_#_TRACTION_MOTOR_INDUCTION

BOGEY_REAR_WHEEL_#_TRACTION_MOTOR_INDUCTION

BOGEY_FRONT_WHEEL_#_TRACTION_MOTOR_UNIVERSAL (Commutator motors that run on both AC and DC)

BOGEY_REAR_WHEEL_#_TRACTION_MOTOR_UNIVERSAL

FRAME_WHEEL_#_TRACTION_MOTOR_UNIVERSAL

For internal combustion locomotives:

SUPERCHARGER_#

TURBOCHARGER_#

CHAIN_DRIVE

HYDRAULIC_MOTOR_#

HYDRAULIC_PUMP_#

HYDRAULIC_RETARDER

FRAME_WHEEL_#_TRACTION_MOTOR_HYDRAULIC

BOGEY_FRONT_WHEEL_#_TRACTION_MOTOR_HYDRAULIC

BOGEY_REAR_WHEEL_#_TRACTION_MOTOR_HYDRAULIC

For electrics:

TRANSFORMER

CIRCUIT_BREAKER

TAP_CHANGER

AC_MOTOR_# (Not a traction motor, used for motor-generator electrics)

RECTIFIER_MERCURY_ARC

BOGEY_FRONT_THIRD_RAIL_SHOE_SIDE

BOGEY_REAR_THIRD_RAIL_SHOE_SIDE

FRAME_THIRD_RAIL_SHOE_SIDE

PANTOGRAPH_FRONT

PANTOGRAPH_REAR

PANTOGRAPH_FRONT_BASE

PANTOGRAPH_REAR_BASE

PANTOGRAPH_FRONT_PALLET

PANTOGRAPH_REAR_PALLET

PANTOGRAPH_POLE_FRONT

PANTOGRAPH_POLE_REAR

Single-arm pantograph parts:

PANTOGRAPH_FRONT_GUIDING_ROD

PANTOGRAPH_FRONT_UPPER_ARM

PANTOGRAPH_FRONT_LOWER_ARM

PANTOGRAPH_FRONT_COUPLING_ROD

PANTOGRAPH_REAR_GUIDING_ROD

PANTOGRAPH_REAR_UPPER_ARM

PANTOGRAPH_REAR_LOWER_ARM

PANTOGRAPH_REAR_COUPLING_ROD

Double-arm ("diamond") pantograph parts would probably be the same except mirroring the single arm parts and animations, and minus the guiding and coupling rods.