I need to find why my lights becomes dim and the motor acts like it is gonna stop running. I got home safe and leave the trouble for day light. When I got my battery charger to charge up the battery. The meter says it is full and need no charging. I went and start the car. Everything works. It does that several times when I drive over 50 miles. No matter day or night and also slow down the wipers and heater. When running heater full blast. It slow down and the motor act like it is not getting enough juice. Turns off heater or lights the motor runs better. Had a new battery put in and the alternator was test to putting peak voltage. Any help with this would be appreciate. Thanks in advance.

My 81 does the exact same thing except for the diming lights. but rpms drop about 300 when lights are on full, also doesnt idle to well with wipers and heater going. I dont really have a clue

Sounds like the main fuse in underhood box is ready to go.

sounds like corrided wires possibility???

Check the voltage of your battery for one... What's the voltage while the car is off. Get someone to start the car while you check voltage, when the car cranks, what's the voltage? While the car is running, what's the voltage. Rev the engine, does the voltage increase?

With the car running, kick in the heater and lights and check the voltages...

It could be your alternator showing signs.

yep, mine did all of that, dumb me thinking it was just the battery so i replaced it, broek down on way home, it was the alternator!!