Nothing happens when I turn the ignition on?

1991 Plymouth Laser 2.0L mileage: 156,000. Turn ignition on nothing, I moved the key around and can hear the starter solenoid trying to engage slowly. It will start once in awhile. I had the starter and battery tested (physically took out and had auto store put a load on it) they both checked out. The owner's manual indicates a starter relay under dash. I called the dealer and several auto parts stores and there is none listed (Mitsubishi Engine). I found three relays under dash above fuse box. Left one unknown, middle one found it was the door lock relay, right one unknown. Manual transmission must have clutch in to start. There is a switch that engages when clutch is pushed in. Since the starter and battery check out, I think I have narrowed down to: 1. Starter relay (if there is one), 2. Clutch switch, 3. Bad wiring harness (+ cable is a wiring harness). Any thoughts?