Hi I think you need to be looking at the TDC sensor as I believe it provides the ECU with speed data also.
No, the TDC sensor is only for ignition timing and engine rpm. This will not give any road speed data, CP.
As for the cruise control - what make is it Phil? If it is the proper Renault accessory it will probably be different to an after market device. Also is the car you are fitting it to, a petrol or diesel, and manual or automatic?
I once had a brilliant after market cruise control and the 'speed' sensing was very easy and novel. The cruise computer simply took a feed from the coil on a petrol engine so that it could sense the rate of ignition pulses at the instant you pressed the button to cruise at the speed you were doing at that moment. Then the cruise computer would maintain that pulse rate. This means it would accelerate the car if the vehicle started to slow, or back off if it started to go quicker, and because of the speed of the computer it maintained the desired cruise speed extremely well, simply by keeping the ignition pulse rate stable at the rate when the cruise was set. Very simple but very effective.
Other devices may require a connection to the speedo output from the gearbox.
But none of them need to actually know the actual speed because you don't set a speed and expect the computer to take you there. You select the cruise at the time you are doing the speed you want it to maintain. The cruise computer will attempt to maintain the rate at the instant it was set. It won't know what that speed actually is, but it doesn't need to know it. It just needs a signal that is related to the speed the moment it was set, so it can maintain that. It could be a sensor by a drive shaft that measure the rate of rotation of the shaft, for instance. The computer will then try to maintain those revolutions and therefore it will maintain that particular speed.
So another cruise control kit had a small magnet which you fastened to a drive shaft and you mounted a sensor near to it to detect it as it rotated.