i have a new altenator and new and really good battery. but when i turn on my lights, my power goes from 14 to 15 volts to 12 or 11. also dims everything inside my car.

 

If it's a 87, I'd check the small plug on the back of the alternator to see if it's on good.

If it's on good, I'd turn the key to On, pull the small plug off the alternator, and put a voltmeter on the black/white wire in the plug, and see if there is 12v there. Should be there.

Actually it sounds like one of the three diodes in the alternator is kaput. That's just a guess.

Another thing you might try. PUll the positive terminal off the battery. Then go to the alternators large wire and see if the nut is on good and if there is corrosion around that wires terminal.

If, when you turn the key to just ON, the idiot lights should light up. That act would prove the small plug on the alternator is connected. It won't tell you if the black/white wire has 12vdc though. Don't confuse the black/white wire with the white wire with a black stripe.

 

i can tell u that, my big black cable of the altenator isnt corroded, but melted a little cause the nut came off. what does that wire do anyways. does it hook directly up to the battery.

 

That wire goes directly to the fuse box in the engine bay. It connects with a nut on the aft side of that fuse box. That wire also goes directly to the ignition key. The black wire at the ignition plugs about a foot below the ignition key.

I'd suggest removing the positive battery terminal before fooling around with that wires attachment at the back of the engine fuse box. To much chance of arcing something with the batt connected.

 

are you going by the stock gauge or a multimeter?