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.

i will pull the battery and have it checked

Cucu:
I pulled the battery and took it to a local parts store. The boys had a $1500 electronic tester.... Anyway the battery checked out excellent.
I thoroughly cleaned up the terminals and battery cables and reinstalled the battery and rechecked the VR blue wire voltage. There is still a 1 volt drop from the battery to the VR.
Where do I go from here?
Glenn

you need to find where the drop is coming from. it has to be some where there is a connction. eith the starter relay on the fender, the fusable link may be bad (resistive but not open), the bulkhead connectors, eyc. just get a schematic and trace the wire from the VR back to the battery.

a way to check to make sure Im not sending you on a wild goose chase is to rig up a jumper to the Blue wire. start the car and watch it over charge, then connect it staright to the battery post (so you eliminate ALL the connections). if the charging goes down to normal, you know the cars wiring has a bad connection somewhere. the trick is finding it.

Update:
Cucu, I stripped off a little insulation off the blue wire a couple inches below the VR plug and spliced a jumper wire to the stripped blue wire. The jumper wire was a heavy stranded wire to minimize voltage drop. Anyway the voltage is 15.1 volts through the normal bulkhead circuit and 14.9 volts through the jumper.
I was expecting a bigger drop... Should the voltage be between 13 and 14?
I pulled each field wire off the Alt, one at a time and voltage dropped from 15.1 to 12.9.
What do you think? Could it be a problem in the new harness?

yes, the voltage should be 13-14v. but right now your battery is at 12something so it may be trying to charge the battery.

when I go home tonight. I'll put a meter on mine and tell you what Im getting. In the meanwhile. put a battery charger on your battery and charge it up for a while making sure you dont dump too many amp into it (limit the charger to 10 amps max)

you may have just a weak battery causing the alt to push out some volts or the Voltage regulator may be bad.

in the meanwhile take out a bolt on the VR and make a ground strap to make sure you have a good ground.

ok, im home and i made some measurements. car hasnt been started in a week.

With the engine off, Ign off i get (all measurements made with the voltmeter neg lead on the batt neg post)

V @ batt = 12.5v
V @ alt out = 12.5v (notice it is the same as the voltage at the battery. it should be)
V @ Alt Blue field = 0v (it should be 0v cause ign is off)

With the Ign ON but the car not running, I get

V @ Batt = 12.4v
V @ alt = 11.92V (The load from the ign plus the resistance of wiring is pulling down the batt voltage slightly. thats normal)
V @ Alt Blue Field = 11.2 v (no comment)

With the Ign ON, and Car running at 600 rpm

V @ batt = 14.11 v (alt is charging the batt)
V @ alt out = 14.3 V (alt voltage is slightly higher than Batt cause of wiring reistance between alt and batt. its normal)
V @ Alt Blue Field = 13.8V (since the alt field (ie, the ign voltage, is 13.8v, , the VR will charge slightly but not too much. just enough to maintain the battery and run the car stuff)

With the car at 1400 rpm, the V @ alt Bleue Field is 14.0 (its still maintaining. not overcharging).

Turn car off

V @ batt = 13.2 V immediately and decays down to 12.7v after a beer or two.


v @

Hi, guys, I've had some 'puter problems and haven't been following this. Cuco has given you some EXCELLENT advice. It almost sounds to me like that as you've been moving/ wiggling stuff, etc, you may have "made" a bad connection better.

I CANNOT STRESS ENOUGH both cucu and myself, the advice we've given re: checking voltage drops, that is voltage loss UNDER LOAD through various wires/ connections, etc.

The firewall/ bulkhead connections on these cars have become just about the no1 suspect.

and one last time YOU CAN NOT check a regulator ground with an ohmeter. That is because current causes voltage drop over resistance called "ohms law" Let's say you have ONE TEN TH just ONE TENTH of an ohm resistance between the battery negative (post) and the regulator case. With some 60 amps (or more) ohms law says thus:

I (current in amps) = E (voltage) / R (resistance)

Transposing, E = I x R

so Voltage = 60 amps X .1 ohms

You now have SIX VOLTS DROP over that one tenth of an ohm

The point? You can measure the voltage drop under load, but YOU CAN NOT measure one tenth of an ohm with common meters.

Additionally, many drop problems are through corroded/ intermittent connections, which do not show up until heated up and loaded under current.

One more last point. YOU CAN NOT check high-amperage diodes in alternators with an ohmeter, even ones with a "diode check" feature.

YOU MUST check high current rectifiers by running considerable current--10-30 amps through them, and once, again, checking the voltage drop!!!!

absolutely!! voltage drops are the way to diagnose electrical systems. Ohms will tell you if you have continuity...well thats wonderful, but it won't tell you if it can take any amount of current!

Thanks '440sixpack, cucu et al. Your help is much appreciated.
I plan on bypassing the bulkhead connector on the high current wires and will make sure the Voltage regulator is grounded. Is there a test to check a VR for proper function.
Funny thing is I worked as an electrican for a couple years and spent two years in school studying electrical construction. That was 1981 when I was 21. I am used to a white neutral wire to complete circuits.
Glenn