I took the barracuda out for drive on satuday and when I got back, battery was cooking. I checked the alternator out put and battery voltage and the voltmeter was pegged at 15v. I pulled the alternator and dropped it off at a local shop. The guy who tested it said it was fine and that it has to be the Voltage regulator. He suggested the alternator will not cause an overcharge problem. I picked up another voltage regulator and reinstalled it with the old alternator. Still has 15+ volts at idle.
Was the auto electric shop guy wrong about the alternator? Can it cause a overcharge problem on it's own? What other possibilities?
Thanks
Glenn

Actually "Rapid" that may not be correct.

WHAT YEAR is the regulator/ alternator?

If you have the later (70 and later) regulator, IT COULD BE the alternator causing the problem, IE one end of the field could be shorted to ground, or the regulator side brush could have become shorted to ground

If you have the 69 and earlier, it's either the regulator, or a poor ground between the regulator and body OR

poor supply voltage to the regulator (ignition terminal)

FIRST QUESTION: WHAT YEAR is the regulator??? 69/earlier, or '70/ later?

You guys don't want to do this, but---you've replaced the regulator, so it's probably OK

Take a meter----

With the car running at high idle--simulating "low/med cruise"

stab one meter probe DIRECTLY onto the regulator body. Stab the other probe DIRECTLY onto the battery neg. post.

With the car running as above, You want THE LOWEST possible reading, NOT MORE than .5 (1/2) volt, and the less the better. Higher shows poor ground between the regulator/ body/ engine/ battery.

SAME THING with the ignition feed to the regulator.

Stab one probe DIRECTLY onto the batt. pos. post. Stab the other to the ign1 feed to the regulator/ ballast. AGAIN you want the LOWEST possible reading, a few tenths or less NOT MORE that 1/2 (.5) volt at the very most. More than this shows a drop somewhere--corroded wiring, connections, bad bulkhead connector, bad connections at the ign switch, or a bad switch itself. Could be bad connections through the bulkhead going to the ammeter, loose connections to the ammeter itself, or even a bad "permanent" splice in the harness itself--I found this on at least three cars "back in the day"

It's the 72 and up (or square back )alternator. The volt regulator is one I picked up from Napa yesterday for $14. I am assuming it's the 70 and later one.
Both screws holding the Volt regulator to the firewall were stripped in the holes. I will work on the ground this evening.
If it's not that maybe a new alternator
Glenn

You also need to be sure what the voltage is at the blue wire at the regulator. The regulator reads that wires voltage to control the charge rate. So that wire can not be fed through a resistor. The moulded plug on the regulator can also fail. No voltage to the regulator on the blue 12 volt switched wire will also cause overcharge.

The car is a 70 cuda with a 72 and later style square back alt and a 70 up style VR . There is also a new M/H / Year one engine (dual ballast)harness.
Cucu, If you recall, I had a problem with coil voltage when I installed the new harness first. There was a voltage drop from the battery to the ballast. This may all have something to do with the harness.
Now that I am armed with useful Info, I will do some test and report back with the results. Thanks Guys
440sixpack, it's not my normal path to "THROW PARTS" at a car. I have areas of strong knowledge and areas not so strong. I know the basics about auto electrical, but that's it. That's why I am here asking questions....
Thanks Again
Glenn

ok, its starting to come back to me....

if you have a voltage drop at the ballast, you probably have a voltage drop at the VR as well. the most likely culprit is the bulkhead connector. as tese cars age, the connectors get oxidized and/or corroded and that cause resitance which will drop the voltage as the resistance increases.

as the system voltage drops, the VR thinks you need a charge, so it tells the alt to kick it up a notch.

check the voltage at the battery. and then, Check the voltage at the Fuse block under the dask on the BAT spade terminal. then check it at the blue wire at the VR.

When you check it at the VR, check it with the blck meter lead on the battery - terminal and then try it with the black lead on the case of the VR (that will tell you if the VR is grounded well enough)

Thanks Cucu. I grounded the VR well. I checked it with an Ohm meter to different parts of the engine bay and it is definitely grounded.
What in the heck are you doing up this hour in the morning? It's 8:30 am here in North atlantic. Must be 5am where you are.

im workin over here!

Cucu Et Al:
Ok, I ran home lunch time and checked a few things. With the ignition in the run position but the car not running, I have:
12.5 v battery pos to battery ground
11.3 v VR blue wire female connector (disconnected from VR)to batt ground
11.3 v Alt blue wire (disconnected from alt) to batt ground
10.2 v Alt blue wire (connected to alt) to batt ground.
I never got a chance to crawl under the dash yet...will check fuse block batt spade this eve.

Following is FYI
1. When I changed the wiring harness I inspected the engine side bulkhead connector. Every thing was in good shape... no corrosion on the engine side so I packed the connectors full of dielectric grease and buttoned it up.
2. I also ran a a piece of #10 wire (with 6" fusible link) fron the alternator batt post to the starter relay batt post.
I have that disconnected right now till i sort out this problem.
3. The M&H/ Y/O wiring harness, as previosly mentioned was a 4 pin ballast unit. I had 3 volts at the coil. I plugged the ballast connectors into a 2 post resistor, eliminating the Aux circuit and got 8 v at the coil, and thought the problem was solved... Obviously not

try those same reading with the ballast resistor disconnected (that same blue wire will feed the ballast and the coil)

Cucu:
I checked the battery blade on the fuse box...around 12.4v. Same as the battery.
Then I disconnected the engine wiring harness from the bulkhead connector and checked the female connectors on the firewall.
With the ign in run position, I got 12.9v at terminal 18 and 23.....and 12.9v at the battery. One is to the Alt and the other feeds the Junction for the ballast, etc. Funny thing is with the engine wiring disconnected the voltage all over jumped .5 volts. When I plugged the harness back in there was a voltage drop of .5 volts again.
I will run out now and do the same checks with the ballast wiring disconnected....back shortly

OK , Here goes
With the ballast resisitor completely disconnected and the Ign in run position:
Battery- 12.4v
V/R blue wire- 12.4v
Alt blue wire (disconnected) 12.4v
No voltage drop from the battery to the VR and the alternator with the ballast offline

Glenn

so that tells me you probably have some resistance in your wiring between the battery and the VR. most likely at the bulkhead connector.

the reason I can say this is because when you have the coil connected (when the ballast is hooked up), the coil loads the system and draws current. The resistance in the wiring causes a voltage drop. thats why when you disconnect the coil, the voltage at the VR reads the same as the battery (the meter does not draw current- it is high impedance and looks invisible to the system).

basically, the bad connections you have act like a resistor and is dropping your system voltage.

when the car is running (ballast and VR hooked up) what is the voltage at the Blue wire at the VR?

also, the .5 difference in voltage tells me your battery probably needs a charge. it shouldnt drop half a volt with no load other than the harness hooked up. Use a charger and slow charge your battery. it may be bad. can you have it tested?

Glen you need to have the eng running at a fast idle to check for voltage drops. With no current flowing high resistances(if present) do not restrict anything.

the reason I had him disconnect the coil at the ballast and check the voltage at the VR, was to see if maybe there was something ELSE drawing current and dragging down the voltage.

Since the voltage came back up with the coil disconnected, I kinda halffast checked for other drains on the system

Good morning Cucu:
Where is the best place to start checking? At the battery and work my way forward? What did the lack of voltage drop at the battery blade on the fuse box tell me? What if I bypassed the bulkhead on that hot wire and went with a solid connection?
I can pull the bulkhead connector and check it
The battery is probably fried. It's been over charged for a while.
Thanks
Glenn

the first place i'd start is with a new battery. if its fried, it will throw everything off. internal resistances will create voltage drops that will be telling your charging system to charge.