It's possible!! If you have a meter, set it for "Ohm" reading. Take a reading of the cables and find which one is "Ground". The one that is ground will have a reading of 0 (zero Ohms) and the other will read "OL". You may want to label that cable or put some black electrical tape on the cable that is ground.
Place one lead on the cable and touch the other to a clean ground on the tongue. Anything that is not painted. You can use one of the bolts one the tongue jack. It will read zero ohms ("0") or anything close to zero such as 20 Ohms.