For the last few days I have been having an issue with my 98 f150. When I turn the key, sometimes all I will get is a click. It has up until today, eventually started. Today when I got home from work and pulled into my driveway, the truck began to screech very loudly. I shut it off and tried to restart. Again all I get is a click. Battery is good, and posts and conections are clean.
I just went through this with my '94 F150 (5.0L, 155k mi, not that that is relevant to the fix).
Ford used a flag terminal on the starter solenoid (on the starter itself) in 1994 and other years and used a 12 gauge wire from the starter relay (on the right fender) to carry drive current from the relay to the solenoid by way of a 1/4" quick disconnect. For weatherproofing they used a rubber or plastic boot over the quick disconnect, but in the starter's environment the boot eventually disintegrates and leaves the flag terminal to corrode. Which it does. And it quits passing current when that happens, leaving the relay to make a soul-stirring "KLUNK!" When the driver turns the key but with no equally soul-stirring "wrrwrrwrr" from the starter.
I got by for several years by diving under the right side of the truck, reaching blindly into the engine bay, and sliding the quick disconnect off and on the flag terminal to scrape the crud (technical term) off the flag terminal so I could get home. In the snow. And slush. And rain. With air conditioning condensate dripping into my right armpit. And sand in (what's left of) my hair.
Ford did an engineering change to replace that rotten flag terminal on the solenoid with a conventional threaded post and that rotten quick disconnect with a conventional ring terminal. When my starter refused to turn over this last time I swore at it, used a come-along to drag it into my driveway from the parking spot by the house, and bump-started it then went into town and bought a reman starter with the stud so I could replace it. Now when I hit the key the engine spins right over and fires right up -- and I don't need to keep messing with the quick disconnect and the flag terminal to get it to start.
A few notes: keep your torch, right-angle drill, left-hand drill bit, E-Z Out, penetrating oil, and automatic center punch handy when you start this project. Buy some anti-seize when you get the starter. Also, upgrade the starter bolts to Grade 8. Bolt size is 3/8-16 x 1-9/16 (AKA 3/8-16 x 1.5625) although 1-1/2 or 1-5/8 (+ or - 1/16 inch) will also work. (If you're using hex-head bolts instead of flange-head, plan on installing a Grade 8 flat washer under the bolt head and lengthening the bolt by the thickness of the washer.)
Apply penetrating oil to the bolts before you start wrenching on the starter. If the top bolt breaks when you try to remove it finish removing the starter from the engine then heat the inside of the bellhousing where the bolt threads in, oil the stub sticking out, and repeat several times before you try to remove what's left of the bolt. Not too hot; after all, the bellhousing is aluminium.
When you install the new starter, use the anti-seize on the bolts. You will thank me the next time you have to replace the starter -- believe me.