overcharging

76 duster..14.7 at idle climbs 15.5 with rpm increase. new-charged battery. used alternator.
battery voltage is 12.6..checking the ballast resistor blue wire key on at run i have 11.8 and same back probing blue wire at regulator plug. if i unplug the regulator i get 12.4 at the ballast and at the regulator plug blue wire, almost full battery voltage. after plugging reg back in and going to alternator i have 12.3 at alternator blue and 1.9 at alternator green. i unwrapped the harness between alt and regulator plug and blue and green wires are ok,no melt and have continuity on green wire from reg plug to terminal end. is there a short? or bad regulator?

Battery voltage should match alternator output stud voltage. If it doesn't then the wiring between the alternator output and the battery and anything inline with it such as an ammeter is suspect. Is your fusible link good?

what supercuda says is true, you should be looking at wiring issues between the battery and the vr.

it passes through the bulkhead from the battery to the amp meter, to the ignition and then back out the bulkhead again.

Also be sure you are using the same reference for ground, as that can change your readings too.
in case that doesn't make sense, if you are checking the vr, don't use the battery as ground. use the bolt holding it on the firewall as ground, unless you added a ground strap.

or voltage at the alt, field wire, use the alt case as the ground for that voltage.

In theory this should not change the reading. in practice bad grounds will cause different voltages, especially at the vr.

But that is nearly a 1 volt drop, which will screw with your charging system.

run an 8 ga jumper line from batt positive terminal to the alt "batt" threaded stud & see what you get at the battery at a fast idle. EDIT (much) easier yet, hook your large "regular" jumper cables from the batt pos/neg posts over to the alt "batt" stud/housing case (have a helper hold the ends at the alt) & fire it up & see what you get at the batt & the alt. 15+ is way too high for a charged battery. You might even get a handfull of HF mini jumpers with alligator clips & feed the reg/alt field circuits including ground paths & see what develops. this takes everything out of the picture exc the hard components: alt/reg/batt.

voltage when running is same at bat and alt output 14.7 at idle.
figuring this loss of 1+ volt to the blue side of regulator from ballast to regulator when you plug it in is a head scratcher.
i have a 1973 fsm but apparently bulkhead in my 76 isnt the same.
im assuming the heavy blue feed exits bulk head and goes to alt and ballast and the smaller gauge blue from regulator is spliced into it along the way ? i did a recent engine install must of done something to wiring some were.

The voltage on the blue line should be the same as at the battery + and the alternator output stud. That;s what the VR uses to determine the required alternator output. If it is reading low then it will try to run the alternator harder to bring the voltage up. Probably dirty/loose connections in that line. I usually remove, clean, tighten and reinstall them.

Yes the blue wire (ign1) out from the bulkhead feeds the alt (blue wire) field terminal/reg top triangle blue wire connector/upstream side of ballast/ECU power in terminal likely red if OE/blue yellow on MP ECU connector pigtail/even elec choke if used. Grab your meter!

When I finally gave up on chasing the drop, I used that line to feed a relay instead to power directly from the battery to the vr.

but yeah, grab a meter and start checking to see when you get a change working your way back.

http://www.mymopar.com/index.php?pid=28

at least the diagrms.

finally seperated everything out, disconnected bulkhead and fed battery volts from there out still same issue. so i ran everything from the battery and eliminated all harness wiring and it works that way. battery 12.4 down a bit from testing and 12.3 at the field terms and output running 13.6-14.

now either go through harness looking for problem or or do a wire feed from some switched source.

I would use a relay controlled by a switched feed and use the relay to send the blue line voltage from the battery.

at a fast idle the batt is 12.4/12.3 & the alt large batt terminal is 13.6-14, correct? post everything what you have jumped/fed/bypassed.

I chased the same problem all over my '62 for more than a year. I tried everything. I finally gave up and installed an adjustable voltage regulator. Problem solved.

12.4 at rest and 12.3 at the field terminals. idle was 13.6 at battery and alt bat post. ran direct from battery to field term with a splice to volt reg and a new wire replacing the green from alt to reg.

By "at rest" do you mean engine not running? Because your descriptions are confusing. The idle numbers look good, did that fix what you were seeing?

do you realize that 12.4 at rest is roughly only a 75% battery charge ? a 100% charged battery is 12.73 at rest. perhaps your battery is gone, causing your problem[s] ?

heres the rundown.
the battery is less than a year old and was charged overnight with 6 amp charger,yes i realize charge is now down 12.4 as noted.
initially battery with car not running was 12.6. after starting car 14.7 at idle at battery and alternator bat stud- increasing rpm it went over 15.
checking anywere in the charging circuit from bulkhead to ballast to volt regulator to alt field terminals showed a loss of 1 to 1.5 volts between the battery and test points with key on and not running.
bypassing/disconnecting the blue wires and running from the battery only to alt and volt. reg i now only lose about .1 of a volt at the test points(various gauge scrap wires just temporary alligator clipped at connections) and running idle voltage is around 13.6 and climbs to 14.2 with rpm increase.
so i will charge the battery run new wires and as advised power the circuit off a relay and hopefully end up with low 13 ish volts at idle and 14.5 or so max.

You should really find the resistance because its probably not just the ignition circuit. Check the alternator output's connection through the firewall first. The reason is that goes to the main junction - which is a big welded splice that feeds everything. So resistance at the connector effects everything downstream.

'76 is a little different than the earlier years, but the overall concept is similar. When the engine is running, alternator is usually the highest voltage source anything drawing current gets it from there. If its an item that's on keyed 'run' then it goes from the welded splice to the ignition switch. One of the differences you may find is there are two welded splices. It split the load before the bulkhead connector (assuming its running on alternator power, not battery).

PS. To find voltage drop caused by resistance, current must be flowing through the wire in question.

With the engine off, lights off, there's no flow. Voltage in all the hot wires will be the same regardless of condition.

The above drawing may not be correct for your car.
I was helping a kid on FABO who posted some pictures of his 1976 A-body. These were very helpful. Comparing his pics to the wiring diagrams from a factory service manual, it looks like at least some 76 models got an externally shunted ammeter.

If you don't see a drop in voltage between Alt Output stud and Battery during charging, the main wires ( A1 & R6) must be well connected.*

That leaves the connections from the main power line through to the voltage regulator as the places that must be causing a 1.5 V drop.

*Voltage drops only occur when current is flowing through a resistance, so checking when the battery is fully charged, or when the engine is off will not reveal anything.

When running.
Current flows from the alternator through wire R6 through a 14 gage fusible link.
At the junction of the three links, current may divide. Voltage stays the same.
Current for the ignition and field flow through wires J1 (red) to the ignition switch. (There's probably a connector at the bottom of the steering column, but not shown in my schematic above)
From the switch it flows through the blue wire, dividing at the first spliced junction.
The portion going to the field goes up to the alternator. A smaller wire is spliced in for the Voltage Regulator to know the system voltage.
Current for the field goes through the alternator, out the green wire to the regulator, which, when allowing max current, lets it go directly to ground.

thanks for the info.
the harness isnt hacked up but i think its reached the end of its life.
everything is dry,brittle and bulk heads are corroded.
instead of searching for the bad connection i think this winters project will be a rewire.

NAPA has the male/female brass terminals (725147/725145) & they are 99 cents ea but you can get them elsewhere in quantity for less. there is a slight trick for getting em in/out & both bulkhead halves to fit good when done, just holler when the time comes.

You could also just have a bad connection somewhere in your system. I had a 71 Challenger. It would actually cook the battery. I chased all the wires under the hood and the dash. Finally one day I was laying under the dash just looking around and saw a black streak in the connector for the steering column to the main harness. It was the main (heavy) red wire. The connection was bad. I snipped the wire off on both sides and used a "butt" connector to make the connection. Solved my problem. Charging went back to normal.

Look at all your connections. Pull them apart. I could not pull that one apart. I was lucky it didn't burn the harness up.

^^^ agreed, you VOM is your best friend right now. fast idle voltages.