Electrical issue with AC ON
 

Hi, Having few issues when I turn on the AC. After using some time my RPM Start fluctuating slightly up/down (But does not shut the car off) If Night when I turn off the heard lights it becomes normal, after some time RPM Starts moving, then Turn off the parking lights, it gets normal again.

Few further things I noticed that turn on Double Indicator, I feel the load on speedometer lights..dim/glow as indicator works. And when I horn, it dims the head light...Not too much but can be feel.

besides that My battery is 2 and half year old.

Will appreciate early Answers or suggestions.