Alternator failure can produce many strange symptoms. For one thing, the tachometer gets its input signal from the alternator so will cease to work. Misfiring, stumbling and cutting out under power have also been observed in cases of alternator failure. If you are lucky, the ignition charging light will just come on dimly before the real trouble starts -- if this happens, waste no time in replacing or repairing the alternator to prevent a stranding.