1997 Mercury Villager

My 1997 villager won't start. When I turn the key the starter clicks and whines, it's not engaging, I changed the starter and selinod, and had it tested before I put it in. All relays and fuses look good, replaced a couple to be sure, cleaned connections, good battery, still won't start, I can start it if I take cables and connect from the positive battery post to the selonoid, but only when I have a person in the van fully turn the ignition switch and I connect to selonoid at the same time. If I connect to selonoid with ignition in the on position only it will not engage. It's gone me stumped, any ideas. Thanks