84 300 turbo diesel
 

Has anybody replaced just the voltage regulator assembly on the alternator my lights will dim and later will get bright again also the blower motor will decrease speed and speed up and now my battery is dead.

Before you start I would go up and click on the parts tab and find a picture of the Voltage Regulator so you can get a better idea of where the screws go and how you can remove it.

I have not replaced my Voltage Regulator but I did remove it to check the length of the brushes.

For safety reasons disconnect the negative battery cable at the battery.
After that it is just finding enough room to use a screwdriver to remove the 2 screws that hold the regulator into the back of the Alternator.
I used a short stubby screwdriver and I believe it was a Phillips Head type screwdriver.
One of the other members will have to give you the info on what the minimum Brush length is.
After putting the new Voltage Regulator in hook the negative Battery Cable back up.

Before you start replacing parts I would have the battery re-charged and tested for free at one of the Auto parts places.

If the Battery is OK I would put it back in the car and run your car and see if it is charging using a digital Voltmeter (Harbor Freight sells them as low as $3 when on sale).

When you first turn on your Ignition Switch (before you start cranking the Engine) and you do not see the Red NO Charging light on (the engine is not running so it should be Red) it means the Light Bulb is no good or there is another problem with the wiring going from there to the Alternator.
Your Alternator needs a good working Light Bulb in the No Charging Light circuit or it will not charge your Battery.

I agree with nailing down your problem.
I have replaced the VR, two screws, in-and-out. Yet my symptom was a glowing battery light.