Why does my 92 sedan deville lose power when i cut on the headlights or the a/c? on 1992 Cadillac DeVille

When i turn the headlights or a/c back off the power goes back to normal and i am able to gain speed

Asked by for the 1992 Cadillac DeVille
1 answer
poss bad has low voltage and or alternator output is low.