The S13 Seat belt Control Unit is 100% safe to remove, as a matter of fact it is a great idea to remove it when doing the manual seatbelt conversion.
The S13 Seat Belt Control Unit has the following signals, functions and integrations.
-Instrument Panel Seat Belt Warning Light
-Warning Chime (In the USA, M107 (Seat Belt Control Unit) triggers the warning chime. (Specifically via pin #33)
In manual seat belt models, M103(Buckle Switch) triggers the warning chime.)
-Integrates with the 10A Fuse for the Meter and Gauges, Heads up Display Control Unit, Warning Lamps, Auto Antenna Timer, Time Control Unit, Daytime Light Control Unit (Drivers side kick panel)
-Integrates with the 10A Fuse for the Interior Lighting, Radio, Clock, Warning Chime, Time Control Unit, A/T Control Unit, Heads-up Display, HICAS Control Unit, Auto Antenna Timer (Drivers side kick panel)
-LH Buckle Switch
-LH Front Limit Switch (Seat belt Track Sensor)
-RH Front Limit Switch (Seat belt Track Sensor)
-LH Rear Limit Switch (Seat belt Track Sensor)
-RH Rear Limit Switch (Seat belt Track Sensor)
-LH Shoulder Belt Switch (Seat belt Track Sensor)
-RH Shoulder Belt Switch (Seat belt Track Sensor)
-LH Seat belt Drive Motor
-RH Seat belt Drive Motor
-LH Door Latch Switch
-RH Door Latch Switch
Here are the FSM sections which are the most useful for identifying the functionality of the Seat Belt Control Unit.
EL-6
EL-48
BF-32-33
Mentioned here are some of the error conditions that activate the chime/warning light
BF-35
