So my 1996 has been giving me issues. Last year I replaced the alternator because the little 70 amp was unable to drive my lights, heater and wipers without the lights dimming. So I put in a new 120. I began having some weird issues with my alternator about 2 months ago, the wipers would cause the voltmeter to pulse with every stroke as did the signal light, and a code 21. One day I tried to start her up and nothing, I got a boost and she would shut off as soon as the throttle was released. I re-installed the original alternator and a new battery at the same time and she ran fine and the code cleared until last week. Suddenly I started getting the pulsing again and a code 21. I bought a new 120 amp alternator and installed it 4 days ago, she again ran fine until today, suddenly I have the pulsing effect again and another code 21. Can anybody tell me what is going on?