i was driving the car and the battery v was 13.6 .the car then got sluggish and voltage went down to as low as 12.4 . i got home parked it then my door ajar light was staying on (weird) . i start the car again its at 12.8 ,turn on my headlights and it went to 12.4 then the taillamp fuse under the hood went on fire literally . it melted the fuse up and burnt the wires by where they go into the fuse box . what could this possobly be . the alternator maybe ?

Or a short in the taillight circuit.

wasnt the alt .got it checked today . i dont understand how a fuse can just go on fire .its there to prevent fire . the tails havent been touched in a long time .

All it takes to cause what you describe is a poor electrical joint at the connector that holds the fuse. It doesn't take much current to have a high temperature failure like that if the resistance of the joint is very high.

If it had a poor connection it will get very hot and start melting wires and material around it all while the fuse itself is okay. Corrosion is usually the culprit followed by a loose or poor crimp on a connector. It's not all that uncommon as vehicles age.

The fuse will not blow unless the load through it exceeds the max. rating which I'm sure it didn't because the high resistance connection would not allow enough current to pass. You still could find a problem on the tail light or marker wires after you fix the fuse holder but you won't know until you fix that first.

still having problems . i replaced the fuse holder and fuse in the engine bay fuse panel . i replaced the green/white wire from the trunk to the hharness connector at the back of the interior fuse box . that green/wht was burnt all the way to the back of the car . i then tryed it twice and blew the tail fuse under the hood twice . the third time i disconnected the harness that plugs into the back of the interior fuse box (which green/white wire that burnt is on . tryed the light and they all worked (all meaning ,tail markers,sidemarkers,licenceplate,cig lighter light etc) exept for the passenger side tail .it didnt blow the fuse . now i put the harness back in and it blew again . what could this be ? Its driving crazy trying to fix it . azdave come to my rescue !

vote me for the idiot of the year award . finally found the source of the problem .the wires that go to the pass. side tail bulbs were pinched between the tails and frame . :)

Excellent! Found the problem AND posted the fix :thumbsup

Electrical problems can haunt you for ages.