I have a 2002 Ford Ranger and my tacometro is oscillating does not remain in the same position and the revoluvion is not a couple. The engine is in good condition is only the tacometer needle that is not still.
Check how the alternator is loading, the tacometer takes the signal from the alternator, if the loading regime is even will have to check the tab and cable that leaves the alternator, which sometimes is touched against the empty or depressor pump and peel. Greetings