I've attached the schematics for the 1999 cruise control circuits, and the bottom of this contains the circuit operation steps. Electrically, there's a new multifunction switch on the column, switches for the brake and clutch pedals, and the control module itself. The below description does identify "an electrical harness" (I bolded and underlined it in the list) that may be the unique harness (a "sub harness") you have been discovering in your research, however there does not seem to be a difference to the basic harness installed in your vehicle requiring it to be replaced.
Here's the system description:
- The cruise control system maintains a desired vehicle speed under normal driving conditions.
- The cruise control system also has the capability to perform the following functions:
- Coast
- Resume speed
- Accelerate
- Increase speed in 1.6 km/h (1 mph) increments
- Decrease speed in 1.6 km/h (1 mph) increments
- The main components of the cruise control system include the following components:
- The multifunction switch
- The cruise control module
- The Vehicle Speed Sensor (VSS)
- Release switches
- An electrical harness
- The cruise control modulewhich contains the following components:
- An electronic controller - monitors vehicle speed and operates the electric stepper motor
- An electric stepper motor - moves a ribbon in order to maintain the desired cruise speed. The ribbon is connected by a cable to the throttle.
- The controller operates in response to the control switches located on the multifunction switch.
- Brake and clutch release switches are used in order to disengage the cruise control. When either are depressed, the cruise control system is electrically disengaged, and the throttle returns to the idle position.
- Cruise Control Circuit Operation:
- When the ignition switch is in the RUN position, CKT 41 (BRN) applies battery voltage to the cruise control module.
- When the cruise control module is moved to the ON position, CKT 397 (GRY) supplies battery voltage to the cruise control module.
- When the brake pedal or clutch is not depressed, CKT 379 (BRN/WHT) supplies voltage to the cruise control module.
- When the brake pedal is depressed, CKT 1320 (LT BLU) supplies voltage to the cruise control module and CKT 379 (BRN/WHT) does not carry voltage.
- When the clutch pedal is depressed, CKT 379 (BRN/WHT) does not carry voltage.
- When the cruise control switch is moved to the RESUME/ACCEL position, CKT 87 (GRY/BLK) supplies voltage to the cruise control module. When the SET/COAST switch is depressed, CKT 84 (DK BLU) supplies voltage to the cruise control module.
- CKT 817 (DK GRN/WHT) provides vehicle speed signal inputs to the cruise control module. CKT 451 (BLK/WHT) provides ground for the cruise control module.