I have a 2000 Expedition. It has a radical clicking, so I replaced the solenoid and that didn't change anything. So I removed the starter and bench tested it and that ran fine. I noticed that when I would connect the small wire to the solenoid that's when the clicking would start and smoke from the battery negative terminal. So something is grounding out? How do I go about finding the source of the problem. Also where do the wires go to from the battery and from the solenoid so I can trace them?
You've obviously got a short in the wiring somewhere which is causing the 'clicking' noise in the solenoid. If you're getting smoke from the wire or battery cable, then it's a hot wire that is directly shorted to ground when you attach it. As for where the wires go, well that's the fun part of actually 'tracing' wires. Start taking the harness apart and follow that wire until you find the problem. If you can get your hands on a schematic that would help greatly. Maybe try your local Ford dealer.
GM Dealer Technician For 18+ Years In the automotive industry for 20+