You usually use a pull-up resistor when you have a resistance based sensor (like a cossie water / air temp or a VDO pressure sensor) that has 2 pins, and you have to calculate what pull-up resistor to use based on the voltage range you are putting in and the resistance range of the sensor you are working with. In this diagram the sensor would go where it is labelled "switch":



I wouldn't of thought that gear sensor wont need a pull-up resistor, i'm not sure if it likes 12v up it though! I've not used an emerald ecu before but usually you would use 5v (Vin, usually shared from the TPS + supply from the ECU), the negative (Ground) goes to the common sensor earth pin on the ecu, then the signal (Vout) will go to your 0-5v input on the ecu.