Lights pulsing at high speed/RPMs

the car has done this for a while, but its getting worse.

The car has a little over 100k on it, is stock, with no modifications such as high powered stereo amps, etc.

I have noticed when I hit 70-75mph(~2800RPM) at night, I can see all of the lights pulsing. This includes the headlights, as well as the map lights and the dash lights if they are up to full bright.

the pulsing is hard to describe. it varies in intensity, but about every half second the lights will dim by about 10-20% and then go back up to full bright. it varies each pulse in intensity, and if I back off the accellerator to let the car coast, it goes away. if I reapply power to go back to speed, it wont do it for a minute or two. after sustained high RPMs it will start to do it again.

It also does it whether cruise is engaged or not.

If I slow down below 60 or 70, it seems to go away entirely , and there are no other performance indications except for one transmission issue.

Sometimes the RPMs will drop excessively when sitting at a light like the torque converter isnt fully disengaging. On VERY rare occations the car will want to lurch when sitting in drive at a light with my foot on the brake.

It has done this pulsing for the past 25k miles, but recently the intensity of the pulses has increased dramatically. It started with a “wow, am I seeing things?” to “gee, I wonder if I can make it the hour drive to the end of my trip?”

I think I have replaced the battery since it started, but not sure how long ago.

any ideas? Voltage regulator?

It sounds like a problem with the charging system. Also you want to double check the ground cable between the engine and the frame as well as both ends of each battery cable.

I believe that the brushes in your alternator are badly worn.
Have the alternator output checked before you wind up stranded somewhere.

I suspect the alternator (which often has the voltage regulator, and ac to dc voltage converter (diodes) built in). This can be checked with a multimeter using the ac and dc voltage test settings.