Here is the Data on Cub Cadet Mechanical Voltage Regulators...
1969 Service Bulletin:
Delco-Remy field-service bulletin for L and non-L type regulators.
D-R bulletin # 7275, July 8, 1969
3 Terminal V/R
STANDARD CURRENT-VOLTAGE regulator often used in cars and trucks. A regulator
without the “L” terminal is unsatisfactory for tractor use because the low voltage settings
would result in an insufficient charge to the battery during cool weather. This condition is
more pronounced in tractor batteries because their location usually allows them to become
colder (that in autos and trucks). If the voltage setting is increased to compensate for the
cold, the setting will be too high in warm weather.
4 Terminal V/R
NON-STANDARD COMBINATION CURRENT-VOLTAGE regulator with “L” terminal
When a heavy load is used, especially lights, the generator output increases. The
regulator has an extra terminal marked “L” which is connected with the lower contact
point in the cut-out relay. This extra terminal permits current from the generator to be
diverted to the load without it passing through the current-voltage regulator. Generator
output, therefore, is allowed to increase to a value sufficient to handle the load and still
supply charging current to the battery (if limits are not exceeded).