What is the problem when the car starts to sputter when the headlights and ac and radio are turned on while the car is running?

Answer 1

Low Battery Voltage

There could be several causes for the simultaneous use of headlights, air conditioning, and radio resulting in the engine "sputtering." The following description of my findings in my case certainly is not the only cause.

I had this happen some 47 years ago near the end of my nighttime return home from a long trip, and I determined the cause turned out that my generator [this was before alternators were common] had failed.

After a few hours of using a lot of current [headlights, tail lights lights, and radio] out of the battery, the battery voltage dropped so low that the high voltage from the distributor/coil was too low to create a "hot" enough spark to guarantee ignition of the fuel/air mixture in all the cylinders all the time.

Because I was on a back country highway, out in the middle of nowhere, with no help for miles, I was forced to turn off ALL electricity using devices, except the ignition. Fortunately there was a full moon and I was able to limp into my home town and home. I was lucky and had cut it very close as the engine was barely running when I got home.

It is important to note that a defective alternator/generator is not always the cause of the battery not being adequately charged. Other causes could include [but is not limited to]:

• The drive belt maladjusted allowing slippage on the alternator pulley.
• Maladjusted or defective voltage regulator.
• Any conductor [wire] in the charging system either cut, broken, or grounded.

There are probably other causes which don't come to my mind at the moment. Good luck.