I'm new to the forum but not to classic Mustangs. My son and I restored a 67 coupe and we had a problem with the battery holding a charge. The problem seems to be a faulty voltage regulator.

Over the years many parts have been changed and upgraded, among them the alternator and voltage regulator. Now I have no idea what alterator is on the car. It is a Motorcraft but I don't know the output. 38, 42 or 55 amps? Any ideas how to ID the unit? It has no color stamp on it. The voltage regulator was also replaced with an electronic one so there is no Ford number to X-ref.

Any help would be appreciated.

 

Welcome to our classic section of the Mustang Forums. Your voltage regulator has been upgraded to an electronic VR because at some point in time, the alternator was also replaced. My advice is to take out the alternator , and take it to an auto parts place and have them check it to see what condition it is in for your application. The VR is most likely good to go, since it is electronic and not mechanical. Get back with us with what you find out.
On Edit: The VR only costs a few bucks, so while you are at the parts store, just get another VR and plug it in.
On second edit: Have you considered that your battery may have a dead cell or two? Have that checked too.

 

Thanks for the info. The battery is new and checks OK. I opened the VP mainly because I can't help fiddling with stuff. There is a blown resister of the board so its got to be replaced. My only question now is did the resister cause the failure or did something else make the resister blow?

It seems that the resister is conected to the Field terminal but printed circuit boards can be hard to trace so I'm not sure.

I will replace the VR and let you know the results. Again, thanks for the response.

 

Oh, you have a mechanical VR.....If your alternator has been replaced then the VR should have also been replaced at the same time. Your mechanical VR and the alternator weren't talking to each other correctly, that's why the blown VR. This time, put an electronic VR in it.

 

What is your voltage accross the battery with the car on?

It should be 14-16 Volts. If it is near that, you may have a drain on the battery or a bad battery. If you do have the correct voltage at the battery the voltage regulator and alternator are all installed correctly.

My 73 and my 66 had 61 amp alternators.

 

Might be silly but check your wires
Had a battery keep dieing on me in my Ranger cause I had a wire get smashed and wasn't letting enough current thru

 

Although a possibility, he has already said the VR is dead. Good point though.

 

oops, I can't read [8D]

 

Thanks for all the help and suggestions. I changed the VR and the problem is solved. No more battery drain and the car starts each morning.

Thanks again.

 

Glad you got her fixed, and without a lot of trouble and money.