just test the 2 wires that connect to the back of the emblem, one will be negative and one will be positive the emblem will only light up one way, attach some extra lead to those wires and install the emblem, then just locate your needed power source as the other member noted above, pretty easy to do. it's just a led light it won't interfere with anything.
when I bought my chevy bowtie one it came with a install sheet, strange that the gmc would not. the headlight wiring should be the same for a 16 & 18 so not sure why it is not compatible with the stock harness, you should be able to unplug the headlight harness, plug that into the emblem harness and then plug the other end of the emblem harness back into the headlight. then just stick the 2 wires from the led into the supplied harness plug. they only go on once which is why you need to check the polarity first, otherwise it takes a special tool to take the harness apart and re-pin them.