Too Much Voltage

First, I hate wiring and electrical. 1974 Dodge D100. So, installed a new Autometer voltmeter. Wired into the ignition feed and wired to a good ground. Fired it up and it was reading 12-14 volts at idle and 14.5 at cruise. Anyway yesterday afternoon I was cruising down the freeway and noticed the VM reading 16.5, took the offramp and came to a stop. It read 16 at idle. Turned on the lights and it made no differance.

Today I replaced the voltage regulator with a spare I had. Still reads high. Switched alternators and I get the same. Went through and made sure all my grounds are tight. I even added a frond wire to one of the mounting bolt for the regulator. Cleaned up the ground foe the batter6 cable. Had the battery checked, it showed it had a bad cell. So, new battery. Came home and put it all together. Now, it idles at 14-14 volts and when driving it’s back to 16-17 volts.

Any suggestions?

Check the Ign. terminal on the regulator. It "senses" the available voltage and energizes the field windings in the alternator to bring the voltage up. A low reading at the terminal will cause an overcharge condition.
Next I would check the reading across the battery. it "should " be very close to the ign terminal reading.
if not try removing and reinstalling the bulkehead connector at the firewall and repeat the above tests
Report back and we'll got from there

Thanks

Am I checking with a volt meter?

yes use a volt meter.
basically you are checking for a voltage difference in the sensing line or the field line.

1 field line goes to the vr the other ties back into the key on power from the ign 1 on the key.

here is how I look for voltage drops.

with the car on run, but not running.
you check with the voltmeter using the battery ground.
check against the pos of the battery, see what the voltage reads.
then check voltage at the sensing line of the VR.
Then check voltage at the field of the alt. with the vr plug pulled, (assuming this is a dual field alt using the later triangle plug vr), one of the fields will be 0, the other should be battery voltage.
you can then trace back to the bulkhead to see if that is causing the issue or a bad connection somewhere else.

you can also transfer the ground to the body of the vr as well when checking the sensing line voltage and to the body of the alt for the field to see if there is a ground issue.

generally speaking I would bet you will see almost 1 volt drop meaning you need to clean up the bulkhead connector or find the bad connection.
if swaping the ground gives you a bigger volt diff, then you have a bad ground somewhere.

Do you trust that Autometer gauge to be accurate now?
Check it out first against a real good V.O.M.
I've had to many expensive Autometer mechanical race gauge that where NOT accuarte

I should also add the truck idles ok but when put in either reverse or drive the engine dies.

Removing the connector from the regulator creates an open circuit.
No current flows.
The voltage at both connector terminals should be within tenths of the battery.
The only drop would be from the current flowing to the ignition, which is only a couple amps.

In this situation, it probably makes more sense to measuring voltage at the alternator output stud to the regulator input with the engine running.
The closest locations to measure the votlage being sensed by the regulator while running are the alternator brush with the 'ignition' wire, and the ballast resistor connection with the same.
The 'ignition' or 'run' wires are usually dark blue or dark blue with a white tracer. But being a truck, it might be different. Later trucks used a different color, but my guess is '74 is the same as cars of those years.

If the voltage developed by the alternator increases with increasing rpm and vica versa, then it is almost certainly a regulation issue. A small variance at low rpm is normal. But going above 15 Volts is not.
If the second brush (usually connected to the green wire) gets grounded, then there is no voltage regulation. So check the brush terminal's insulator and also the insulation on the green wire to the regulator. If that's not it, then suspect the regulator.

The regulator works like this.

Voltage of the Ignition Wire (J) is internally measured by the transistors.
If it the voltage is low, the connection to ground for the rotor is completed.
Current then flows through the rotor windings creating a spinning electromagnetic field.

If the voltage in the Ignition Wire (J) is high enough, a tiny current is used to break the rotor's connection to ground.

Nice diagram

Ok, dug out my voltmeter. Static voltage on the battery is 12.7 volts. Fired the motor and I get 18.5 at idle. Checked the alternator and at idle I’m getting 18.5, run the motor up at around 1500 rpm and the reading was 22 volts. Took the alternator off and ran down to Orielys. On a short test the machine showed 16.5 volts. Overall the alternator tested bad.

You did good, test, test and test some more until you whup Murphys butt l

Ok, changed out the alternator. Fired it up and it now runs ar idle 13.5 to 14.5 however when the rpms go up it goes to 16 volts. I went ahead a pulled the bulkhead plugs. As suspected both the red white going in was burn’t at the spade and the same for the black wire that goes to the alternator. I have the bulkhead soaking in Evaporust. I did this on a 65 Chrysler I had and the contacts came out squeaky clean. I may just go ahead and replace both the red and black wires, drill out the bulkhead fitting and run the wires through the bulkhead.

I had a similar problem after I painted my Charger. I cleaned up the grounds and added a ground wire to the voltage regulator and all is well now.

Check the plug on the ignition switch. I have seen quite a few melted causing issues. My 77 plymouth had a problem with overcharging and it was a melted blue wire at the bottom of the column grounding out.

Plug on the ignition switch?

On the steering column is a flat plug. The Blue wire on my sons 1974 D200 was burnt. I cut them out and put a bullet connector inline.

As said the plug is near the base of the column. A common fail point on ignition switches.

i have repaired many of those connectors because of a "melty" condition over the years.

Ok, all up and running. I get 14 volts ar idle and 14.5 at cruse. Meter bounces a bit which give me reason to think there’s a hiccup in there. Got home ant had a crappy idle, finally died. Restarted now it dies when I put it in gear. Given I drove the truck hitting bumps leads me toward the bulkhead connector. At idle the battery is getting a charge around 14 voltsI’ll go out and check tomorrow. Also, since we changed out the steering column I’ll be checking that wiring as well.

I was getting really erratic reading when i had my issue. I thought I fixed it only to find out a day later mine was overcharging again. I guess where the blue wire was grounding out it must have become ungrounded for a short period of time then regrounded itself. It drove me crazy. Best thing is to look at the wires at the base of the column and trace some of the wires back to see if you see any signs of melted wire. Also any wires in the engine compartment. It becomes pretty obvious once they start to melt.

Checked the bulkhead connections, all are snapped in tight. Checked both + and - connections on the coil, both appear to be good. Checked connections under the dash, all seem to be secure. I had the voltmeter + wire attached to one of the ignition wire going into the ballast resistor. Since there’s two wires, top and bottom of the BR I’m not sure I have it connected correctly. The voltmeter still fluctuates like the turn signal is on.

BTW, I ruined a red top optima from the overcharging.

Really, Andrew's methodology to troubleshooting was good advice.
The voltmeter fluctuating may or may not be a problem. If its stablizes when just above idle, certainly by 1250 rpm, then it could be normal.
But if there is a difference in the voltage between the alternator output terminal and the regulator's input, that is a big clue there is resistance in the circuitry.
If it the difference increases with lights or other accessories on, then the resistance is in the shared line. The most likely locations of the resistance are in the connectors. A hand hand voltmeter will reveal where the resistance is causing voltage to drop when current goes through them. (When no current is flowing, then the resistance is zero and there is no voltage drop.)
This same technique can also be used to identify resistance in the return (ground connections).

The fact that the plastic coveres are locked together is good, but does not guarentee the terminals inside are making good contact.
The terminals may have backed out when a connector was removed and reinstalled;
or the contact surfaces may have become oxidized, corroded, or burnt;
or the wire strands crimped to the terminal may have become broken, oxidized, corroded or worked loose from crimp.

Being a '74 truck, I would expect it to have been equiped with a dual ballast resistor. But regardless, the feed wires when running will be at, or close to the same voltage as the alternator output terminal (big stud). The coil connection while running will be something less, as will the ECU connection if its still a true 5 pin ECU.
Usually the 'run' or 'ignition 1' wires are dark blue, and dark blue with stripe.
Usually the 'start' or ignition 2 feed to the coil side of the resistor is brown.
But as the '79 truck diagram in the other thread shows, at some point the ignition wire color scheme was changed.,

One of the downsides of any absorbed mat type battery.

When I ran the battery down by leaving the parking lights on, and needed a jump start, I watched the ammeter like a hawk. I kept the rpms to a minimum and added headlights and heater fan as needed to suck off some of the power on the uphills.
Even doing that, the battery got quite hot, and I'm sure its not as good as was before.
I also think that contributed to the early death of that alternator.
About a year later the alternator wsan't producing as much power as I thought it should (noticble at low rpm).
Checking it out on the bench revealed one of the stator windings was open.
Broke at the Y.
While looking for a replacement stator came across this alternator tag.
https://www.forabodiesonly.com/mopar/threads/charging-battery-with-alternator-warning.424783/

The bulkhead connector was soaked in a rust dissolver, rinsed and blown dry. Same done to the engine side. If done this before. The ballast connections are two red wires on top. Verified with my voltmeter. The run side shows power an no power when the truck is shut off. The feed into the BR doesn’t show power unless the key is in the on position.

Proper way to voltage drop test. Hot side; connect the dvom to the battery positive terminal. with the engine running take the other lead and follow each positive alternator connection. Any voltage read on the meter is the amount lost at that connection/wire. Battery? You can do the same with the ground side. Negative post all the way to the alternator case.
This test can be used while varying loads, lights, heater ETC. It'll show up the weak spots quickly.
Doug

So, now that I have the charging issue pretty much figured out the truck now dies when put in drive. Truck idles noramally however when put in drive from park or neutral it sputters then dies. Going to Good Guys tomorrow so I’ll tackle that issue next week.