It only happens when i turn the defrost on and or have the heat on as well. could someone please help me out.

Your power SHOULD drain when you turn things on. We need alot more specifics. Does the car stall? Idle change? What does the voltmeter show?

It start too drain like its going to cut all the all the way off. the volt meter will drop quickly, and the lights will start to dimm

Can you please put your car information in your signature where "Go hard or go home" is? That'll help immensely. For all we know, you have a 5.0 Liter 1984 Bville.

For your problem, I strongly suspect corroded (internal) battery cables. Disconnect both from the battery and pull the plastic boots off (you must remove the boots to see it).

Tell us what you find.

I will let you know a lil later

Along wth checking your cables, these cars love to corrode for what ever reason, the 96-99 SLE'* came with the 140 Amp alternator (IIRC RPO KG5?). There should be no problem with the system keeping up...unless the alternator is getting ready to puke

Again with what Mr. WIllwren said, where is the volt gauge? Kick on the rear defrost AND fan (on high), record your volt reading at idle, then at 2000 rpm'*.

Finally had time get under the hood to see what the problem is and the alternator is about to go so i order one today 140amp so it should be in next week.