A data terminator is a device that should be used at the end of every DMX512data run to prevent signal reflections that could cause degradation and signal errors. Without a terminator, devices may behave erratically and unreliably. The longer the data run and the more devices connected to it, the more critical termination becomes.
Using a male XLR connector (3- or 5-pin, depending on the device to be terminated), solder a 120 ohm ¼ W resistor between pins 2 and 3 (and pins 4 and 5 if using a 5-pin connector). Plug the terminator into the last DMX512 output in the data run.