Route 1 – Head out of tarbert towards scalpay and then turn left up the track past loch laxadale, till you hit tarmac, then turn left and head up road climb toward rhenigadale, after a few miles you take a right turn off the road onto a track leading back to tarbert via loch trolmaraig(sp?)
sorry to be vague, but it's mega obvious on a 1:25000 map – south harris.
The other routes are a big circuit of an clisham, and the singletrack south west of tarbert, again, buy the 1:25000 map and look for the dotted lines, you can not go wrong.
Spend a few hours round at seilebost beach, amazing.
if you email me on greg DOT bowie AT gmail DOT com, i'll give you my mobile number, call me and I'll talk you through it with a map in front of you.
Been about a lot of Scotland on my bike, but Harris is my favourite, just so atmospheric, remote and absolutely awesome singletrack.