You have some misunderstanding on how the systems work. If you are hearing a rapid, repeating clicking sound, like a loud buzzing, that is usually not due to a bad starter. Most commonly it is caused by one shorted cell in the battery, a discharged battery, loose or corroded battery cable connections, or a battery cable that is badly corroded under the insulation at one of the terminals. On Ford products that is most likely to occur to the terminal that bolts to the starter.
The place to start is by measuring the battery's voltage with a digital voltmeter. If you do not have one yet, Harbor Freight Tools has a perfectly fine one for less than ten bucks. They often go on sale for as little as three bucks. A good, fully-charged battery will read 12.6 volts. If you find close to 12.2 volts, the battery is good but badly discharged. Charge it at a slow rate for an hour or two. When you are done charging it, turn the head lights on for about ten seconds to remove the "surface charge" which can give a false "good" reading. Measure the voltage again. If it is close to 12.6 volts, try cranking the engine.
If the engine starts, measure the battery voltage again while the engine is running. You must find between 13.75 and 14.75 volts. Based on these readings, we will figure out where to go next.
Tuesday, October 4th, 2016 AT 9:59 PM