With lights and heater on, it turns the battery light on?

Hello,

The battery light turns on when the battery is not getting adequate charge from the alternator.

It could be due to a bad alternator as well as faulty wiring.
First check to see the alternator output to the battery.

Here is a helpful video that shows how to test the alternator:

https://youtu.be/Z-p4dMJUpUw

Check for any corrosion on the alternator cable. Clean if necessary.

It is possible to have a defective alternator that is not performing as it is designed to underload.

I have attached diagrams for your reference.

Please let me know if you have any questions.
Thank you.