The starter will not kick in on my 1984 Harley Evo engine. What could be the problem?

if its a sportster evo and all you hear when pressing start button is a clicking from under the seat chances are the starter relay needs replacing, take off the seat, undo the retaining bolt, unplug the relay and take it to any auto electrical supplies and get it matched, (or you could go to your local hd dealer, but add a 0 to the price)