When I got my bike the previous owner had fitted a switch for turning fan on & off manually.

My temp gauge is working and can see that sensor near carb on right hand side.

Might be being blind but where is fan sensor.

Trying to figure out what's been done to the wiring.

Cheers

I'm not up to speed on the early gsxr but if there is no sensor in the actual rad Suzi usually put it in the thermostat housing,
You find only one on the bandit which has fan but no temp gauge and two on the later gsxr that has fan and temp gauge.

You find only one on the bandit which has fan but no temp gauge and two on the later gsxr that has fan and temp gauge.

Yes: you are correct when you say that the Bandit does not have a Temp Gauge... But no: the Bandit does have two temp sensors, one sensor for Radiator Fan Control and a second sensor to control the Temperature Warning Light on the instrument binnacle.

Picture of GSF400 Bandit Thermostat housing:

In this picture you can see the two Coolant Temperature Sensors that the GSF400 Bandit uses, one for the Coolant Temperature Warning Light in the instrument binnacle and the other is the Radiator Fan Control sensor.

Suzuki used this exact same aluminum casting for the GSXR400. If you look at it closely you can see there's a third sensor port cast into it (in this picture it's the small, round extension right next to the large sensor on the bottom of the Thermostat housing).

On the GSF400 Bandit this third port would be left solid (not drilled through and tapped with threads) but on the GSXR400 it was opened up, threaded, and a small Temperature Sensor was installed. This small Temp Sensor was wired into the GSXR's ignition control box.