Can't really help with your problem here, I have the lights fitted but not with the triumph harness I did it myself but the bulbs are H3's & from what you say the fault must be in the wiring but if only one bulb is out then I can't see it being the harness, the 12v live side will likely be ok as it is a spade connector but the earth (ground) is to the mounting screw of the base plate of the bulb, try checking this out if not already, I think it's the best bet. Don't let it spoil your trip though.