I need to be honest. This is a mustang question, but I need the help from this forum because you always are super helpful and knowledgeable.

1968 289 auto. I just registered the car after three years of working on it. It has been starting and running fine around tow. The other day, I took it for a ride. I stopped for about an hour. When i went to leave the battery was dead. I Jump started it and got about 1 mile till it died. I sent my son to get my jump pack. I hooked it up to the car and made it home no problem. About a mile drive. I assumed the alt was bad. The gauge in the dash must not be working as it never moves.

So i took a used alternator off my shelf from some ford trucks of the same era i have parted out, I had it tested and it tested fine so i installed it. It is a D5AF 10300 aa. From my online search i see this alternator is used on many engines from 250-429. I think it came from a 240 six cylinder. I charged the battery for about two hours. After installing the alternator, i noticed a black wire going to the solenoid that was broken/ frayed/ burned. I dont know which. I repaired it and started the car.

The car seemed to run fine. Took it for a drive. No problems. I then tested the batt to see how many volts it was producing. Only about 12.5. So now i think the car is not charging because everything I read says it must be above 13.5 volts. If I disconnect the negative off the battery, the car still runs. Which i have read indicates the car is charging. I changed out the voltage regulator with another used one i had but it made no difference.

Obviously, If i accelerate, the voltage meter increases.

Any thoughts? Thanks

 

Sounds like it's charging if it will run with the cable disconnected.

so if your battery is dying that fast it can only mean you have a serious short, or more likely your battery is toast.

you can check for a bad short by turning everything off and touching a battery cable to the post, if you don't get a spark you don't have a short.

 

Thanks for the reply. It is running great and charging now at 13.75 +/-.