How do you connect a starter soleniod on a harley Davidson flh?

That depends on the year of the bike.

On '65 through '88 FLH models, there are three terminals on the solenoid. The top one goes to the battery, the [small] middle on goes to the starter button and the bottom one goes to the starter.

On '89 and later FLH models there are only two terminals on the unitized starter/solenoid assembly. The larger one on top goes to the battery and the small one on the right side goes to the starter relay.