HEY EVERYONE. I HAVE A 1970 MUSTANG. OVER THE COURSE OF 2.5 YEARS...I HAVE HAD ATLEAST 3 DIFFERENT ALTONATERS GO BAD, TO THE POINT WHERE THE CAR RUNS OFF THE BATTERY TIL IT DIES TOO...MY QUESTION IS, WHAT THE HELL IS CAUSING THIS? BAD WIRES? THE ALTS, I HAVE TESTED BEFORE I BUY THEM, SO THAT PRETTY MUCH RULES OUT THAT OPTION. COULD USE SOME INSITE ON THIS, CAUSE IM TIRED OF BEING STRANDED AND REPLACING ALTS. THANKS. HERE'S A LITTLE MORE INFO... 2 OF THE ALTS HAVE BEEN THE CHEAPIES AT ADVANCE AUTO PARTS, THE LAST ONE, REPLACED IN SEP07, CAME FROM AAMCO. NOW BEAR IN MIND, I HAVE BEEN DEPLOYED SINCE MARCH07. CAME HOME ON LEAVE IN SEP, AND THEN AGAIN IN FEB... SO THE CAR HASNT BEEN DRIVEN THAT MUCH, AND THE PROBLEM HAS ALREADY ARROSE AGAIN. I HAVENT REMOVED THE POSITIVE CABLE WHILE THE CAR IS RUNNING EITHER. I HAVE NOT REPLACED THE PLUG ON THE BACK OF THE ALT EITHER. I FIGURED THATS MY NEXT MOVE, BUT WANTED TO GET OPINONS FIRST. AFTER DRIVING ABOUT 30 MIN TODAY, I PARKED THE CAR AND GOT OUT. INSTANTLY REALIZING I FORGOT SOMETHING AT THE STORE. WHEN I TURN THE IGNITION, I GOT THE DEAD BATTERY SOUND. ITS NOW 9PM, SO 6 HOURS LATER, I JUST WENT OUT TO THE STANG, AND IT CRANKED RIGHT UP, AS I SUSPECTED IT WOULD. SO IM GUESS THE ALT IS NO GOOD, IT RUNS ON THE BATTERY. WHAT DO YALL THINK. BUT THATS THE EASY PART, GOTTA FIGURE OUT why THESE ALTS KEEP GOING BAD. THANKS.

 

A little more info please, are you putting on cheap reman ones from AutoZone or Advance?
Have you replaced the plug on the back of the alt? Are you pulling the positive cable while its running? Big NoNo. Post a complete write up and we can get you straight.

 

Check for 12vs at the batt when car is off. Turn it on and make sure that its reading in the mid 13s or 14s when car is running. You have to see if battery is going dead because its not charging or something is staying on inside the car that causes batt to die. Since its a vintage year I would take a good look at all the wiring that goes to alternator, starter solenoid, ground straps from firewall to block and batt connections.