Try a bit of lead training at home before you try to take him out. Let him wander round indoors with a short length of string attached to his collar (make sure you keep an eye on him so he doesn't get caught up). Use plenty of titbits and praise, and occasionally pick up the string and call him to you (don't pull). If he comes to you then give him a titbit. You can also do this at dinner time. Put his food down and hold the string across the room then let him take up the slack and go to his dinner. Also if you have visitors hold on to the string and then let him pull towards them, following him. You can then progress to using the lead in the same way, and he will then start to realise that it is not a sort of punishment, but a means to get where he wants i.e. 'walkies'.
I have to say I d not like harnesses, particularly in this case as you will be putting undue pressure in the middle of his back instead of encouraging him forward. Look at how many dogs you see on harnesses, still pulling their owners and with their backs all humped up.