2000 Mercury Mystique Repair Question
Is my alternator failing?
You can't expect to test anything or find the problem without test equipment. First of all, get an inexpensive digital voltmeter. Harbor Freight Tools has one for less than ten bucks that works perfectly fine.
Measure the battery voltage first with the engine off and holler back with that number.
With the engine running the battery voltage must be 13.75 to 14.75 volts. If it is low it won't be charging the battery. How are you determining the battery is fully charged? If it is you shouldn't need to jump-start it to start the engine.
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With a 100 % battery , the only thing that can cause non cranking would be bad battery terminals or ground circuit connections.
Give them a check. Try using a jumper cable across the battery negative terminals and engine to see if it works.
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