Voltage Regulator or Alternator?

[97sentraguy]

My 97 Sentra's brake light and battery lights come on together when the engine reaches a certain RPM (52 mph in top gear). If I slow down below this speed, the lights go off. I took it to my local parts store, and put it on their machine. Of course, I did this at idle, and didn't think to rev the engine to make the light come on. The charging system checked out OK, and the battery was "marginal". I replaced the battery after all of my electrical components (stereo, AC fan, etc.) started to slow down. After replacing the battery, the light problem continued, but everything seemed to be working fine, so I ignored it. Friday night, as I was heading to work, the headlights started to get dimmer and dimmer, the radio volume dropped, the speedometer quit working, and the car started to die. I pulled over onto the shoulder, and when my RPM slowed to a suitable level, the lights came back on and I was able to make it to work by driving less than 50 mph. I don't want to add to the value of my 120,000 mile car by taking it to my local dealer, but I'm not sure what to replace. Any ideas?

[NISTECH]

you need an altenator, there is no external voltage regulator, hasn't been since the early 80's they are internal to the altenator now.