Car doesn't always want to start.?

I've got an 1988 Mitsubishi Van/Wagon 2.4L that doesn't want to crank.

Now, I'm a handy person (30 years an electrical repairman by trade.) My van has been acting up for quite some time now. When I turn the ignition key to start it clicks. If I turn the key (& release) about ten times (anywhere from 1-20 times) it will start, sounding normal on that "good try."

I've since hooked up the 2 wires (cables) directly to the starter @ the starter solenoid & ran them into the passenger compartment. So to start the car for the last 2-3 years now, I turn the key to try to start the car once the "usual way" & if it doesn't turn on the starter, I keep the key 'on' & use my auxiliary switch (as explained above - directly to starter) and it will always start!

I'm getting fed up with this problem and want to fix it correctly.

Over the last few years (since the problem first started) I've: replaced the battery, battery cable, alternator, and tried 3 new starters (all 'professionally rebuilt units.) The problem will not go away!

I've checked the ignition switch, starter relay, and like I said, the starter works.

Once again, when I turn the key I get continuity at the switch which triggers the starter relay, that triggers the starter solenoid (I hear it click with a 'thump' as it should) - but the starter motor does not even try to turn (it doesn't sound like a low battery slow turning starter - nothing!)

Any good solutions or suggestions?