plsirl

I have a '68 Mustang (with a '91 engine). A while back I started having dead batteries every morning, so I checked for current draw when the car is completely turned off and found about 0.5 Amps. I've been busy at work, so my temporary fix was to just disconnect the battery when I wasn't driving the car (and this worked perfectly until yesterday). Last night, I about 45 minutes into a drive home when my headlights went dim(this happened gradually), so I pulled off the freeway and the car died at the top of the offramp. The alternator is fairly new.

I checked the car out this morning, mechanically everything looks and sounds great. The battery is too drained to start the car (although it did turn over a couple times). The 0.5 Amp draw is still there when the battery is connected, however is goes away when I pull the top fuse on my under-dash fuse panel (this uses the tube-style buss fuses). If I replace this fuse, the drain does not come back UNTIL I turn the key to try to start the car.

Does anyone know what the top, horizonal fuse controls on a '68 Mustang (likely a little different with the newer engine in there, but probably similar). It is hard to read, but I think it says "14A ACCY". I checked all of the electrical connections that I could think of and all seemed okay. Any ideas where this short is likely to be? I'm out of ideas and electrical isn't my strongest skill.

It seemed like driving during the day is no problem, but at night, with the headlights on, there was too much current draw for the alternator to keep up with. I owed a car a long time ago that did the same thing which was caused by a melted wire.

Sorry for the long-winded post. Thanks so much for any help!

67 evil eleanor

Have the alternator checked at a auto parts store or garage.

plsirl

I just now got back from the auto parts store, they checked the alt and said it was just fine. Any other ideas?

Thanks for the reply btw.

valley firearms

You have a short somewhere. I had the same problem with a 67 years ago. I actually took a stethascope and found a dull humming sound coming from the steering column. It was my horn that had the short.
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JMD

Regardless, I would still tend to suspect the alternator / charging circuit. It could cause both issues.

Is the alt internally or externally regulated? Without really taking the time to look the old charging circuit over in a diagram, etc. I kind of think that a bad regulator might cause a small drain as well.

The .5 amp leak is plenty big enough to drain a battery over a period of time, but it would have to be a much bigger short to discharge your battery while driving. So big in fact that it should have made smoke if not fire. This leads me to believe that the charging circuit was not working when the battery died while driving.

It may be possible that the charging circuit became over taxed and stopped working for a while as a result, but I think it is more likely that your entire problem is with the charging circuit.

A quick test forinternally regulated alt would be to put youramp meter between the big post of the alternator and it's respective wire with the key off and see if the drain exists here.

For an external unit it would take a little more work...but the principal is the same.

68FastbackGT

I second the suspicion of the charging system. The 0.5 amp leak is a problem, but not while the car is running. If the alternator is OK, the voltage regulator or the connections between it and the alternator need to be tested. With a changed battery, the voltage regulator should keep the voltage at the battery around 14.5 volts. Another thing to check is your grounds wiring harness grounds in the engine compartment. A rusty interface between a ground wire and ground will cause loads of problems.

plsirl

Thanks a ton for all of the replies.

Here is where I am going to show my true electrical-noobness. My alt has two bundles of wires attached to it by two plastic clips (rectangle shaped, one smaller than the other). This means that is it externally regulated, right? How would I test for current draw here? Amp meter between each individual wire and its respective pickup one at a time? Or does removing a full clip of wires potentially break the circuit anyway?

Thanks again.

p.s. JMD, I would sell my soul for your engine bay (probably doesnt even have a short =P)!

plsirl

By the way, the car does continue to run if I start it and detach the battery cables. Are alts known to be insufficient on one trip, and then work fine on the next? I cant figure out why I'd gradually lose power on the freeway, but then be able to jumpstart the car and have the alt charge enough for multiple starts the next day. Like JMD said, a short that would overpower a functional alternator on the freeway seems like it would at least cause a smell (if not fire). So if the alt was the culprit, why does it work now? I think I hate electricity.

JMD

Sometimes electrical components can work intermittently, and also an alternator can go out "halfway", this can happen if one diode goes awry in the diode bridge rectifier. when this happens the alternator will charge at half output while working at full power. This type of flaw can also cause a current "leak" when the car is not running.

Iam not very familiar with theFord charging system or their alternators so I don't knowthe specific functions of the plugs you mention so I am not much help here. We have converted the 66 to a 1 wire setup, which takes allguess work out of our charging circuit.

I am fairly confident that your issue is in this area but I am certainlynot sure.

If you end up changing your alternator you might consider one of these.

http://store.summitracing.com/partde...p;autoview=sku

This is what we use, the hookup is one wire from the alternator to the battery side of the solenoid.

plsirl

Once again, thanks for the reply! Perhaps my mistake was getting the alt. tested at the store that I bought it from (PepBoys). I think I will take it to autozone or kragen tomorrow to get it tested again. If they are doing the full current load test, it should catch a bad diode, right? I'll update this thread with what the problem turns out to be.