In reply to jmerrick21:
I have led with a harness improvised from slings when I forgot my harness - I basically got a 120cm sling behind me, brought 2 strands together at the front, and one between the legs, connecting them with a big screwgate. Then an improvised chest harness - a 120 cm sling with a twist at the back between the shoulder blades, arms through the loops created, then join with a Krab. Then join the chest sling to the waist sling - I think I joined them with a tied off sling. This stops the waist harness from falling down and keeps the krabs oriented correctly. Wouldn't really have wanted to fall on it, but it seemed to work at the time! But for the negligible weight of a lightweight harness I would just pack one, if you know in advance you might need it. Far less hassle!