15 volts running & idling. What's wrong?

[Cranky]

It looks like you have the old style breaker point type regulator from your picture.
I suspect the breaker points are welded closed, so you get full charging from the alternator (no regulation). This will overcharge the battery and create a strain on all the components. You should able to remove the cover and visually inspect or just disconnect one of the wires to it and check for continuity. You may be able to just clean up the contacts or replace with a new one or a solid state replacement. I think I have one somewhere... Good luck, nice car.
OOPs just read again you had already replaced the regulator. Sorry, probably the alternator but I've never heard of 15Volts? What type of battery are you using?

If the reg was bad and passing full current, it would be doing whatever the alternator puts out.....upwards of 18v or more. I had one that malfunctioned and it blew the fuse in my radar detector was was rated at 18v. Had no idea what was was up until I drove after dark and noticed my headlights were real bright. That part I liked lol.

 

[91r/t]

You asked specifically how to diagnose an overvoltage condition. Voltage drop at the bat terminal on the regulator is the first thing to be checked. It needs to be measured as previously mentioned. There is no-way your 50-yearold original wiring has 0 voltage drop through the bulkhead connector twice, wiring, ignition switch and it’s connections. If you are not going to measure it then your only option is to throwing regulators at it in hopes of finding one calibrated at a lower voltage or open one up (voiding any warranty) and make the mechanical adjustment mentioned.

^^^I am with him....my 68 Charger overcharged a bit and it ended up being the difference in voltage from the battery to the voltage at the battery terminal/feed wire into the regulator. It was only .75 to 1 volt but you'd be surprised how much this can affect charging and overcharging. Get that difference in voltage before you go any further. Mine ended up being two wires wrapped together creating resistance. Easy fix.

 

[soundhd]

66 Belvedere II 361. I'm getting 15 volts to the volt gauge, battery, & everywhere else. Installed new volt regulator, it has good ground, and I'm still getting 15 volts. The green wire on the regulator registers 8 volts, everywhere else: 15. Where do I look now? How do I diagnose this?

View attachment 516584

I just went through this type of high voltage output with my 70 Roadrunner recently. Alternator failed on the way to a weekend car show as I pulled into town. Purchased a "rebuilt" alternator from the only auto parts store in town......got me home (90 miles) after the show but was putting out 15.3 - 15.6 volts. Replaced the voltage regulator but no change. Heard from other Mopar owners that the 'rebuilt" alternators are problem prone so order a new Tuff Stuff American Built with American parts alternator and problem is solved. Runs at 13.5 at idle and up to 14.5 when under a "load".
Good luck hope this helps.

 

[70Bronco]

Last night, drove the car after it had warmed up and it was running about 15.5 volts. Put a power steering pump on and got that going. Started it, warmed it up, and let it idle. Checked voltage--Voltage regulator, 14.15; Fuse box, 14.5; battery, 14.21. Waited a few minutes and checked again--Regulator, 14.0; Fuse box, 14.3; Battery, 14.1.
Today, started it and drove it on the highway. The volt gauge read 15.8 the whole time I was driving highway speed. Parked it, let it idle for a while, then checked it again--Regulator, 14.2; Fuse box, 14.4; Battery, 14.4.

The voltage tends to bounce. Sometimes it moves a few hundredths, other times it moves a couple tenths. The voltmeter does not do this on three other vehicles. That might be another issue, or perhaps a bad alternator?? I'll probably get it checked next.

[Added. If it's not warmed up, at idle it records 15.0 at the Regulator, 15.2 at the fuse box, and 15.2 at the battery.]

 

[72RoadrunnerGTX]

And the measured voltage drop between the regulator terminal and battery post during these various conditions is? How about the regulator mounting and the alternator case, what does that voltage drop measure?

Why the resistance to taking these measurements? No pun intended

 

[mopar 3 B]

Must have way to much time and nothing else to do. If it keep the battery charged and the lights on there is not a problem.

 

[70Bronco]

Must have way to much time and nothing else to do. If it keep the battery charged and the lights on there is not a problem.

Looks like several drivers have the same conditions and have experienced no problems.
I might try to adjust the regulator I took out to keep the maximum voltage below 15.5. According to the old shop manual, it's a matter of bending the tab with a spring on it. I have two volt regulators, so there's not a lot to lose.

 

[70Bronco]

Ignition terminal on regulator to positive post on battery: 0.21 (or -0.21 when leads switched).
As for the alternator case to regulator mounting--if you mean the regulator mounting bracket on the fire wall, it's 0.0.

Electrical systems are not my forte. Between an understanding gap and other life activities, delays occur.

 

[soundhd]

Well I guess I jumped the gun a bit here (see my reply to the original posting below).
When I first installed the Tuff Stuff Regulator all I did was start the car and let it run at idle and the voltage regulator was showing just over 12 volts so I thought it was fixed. Well this morning was the first time I had a chance to drive the car and it jumped back up to 15.3 volts when driving Called Tuff Stuff and come to find out that when one purchases a new Tuff Stuff alternator one needs to also purchase a Tuff Stuff Voltage regulator..was told they are made to work together. So I ordered one today and will post the results when I get it installed.

I just went through this type of high voltage output with my 70 Roadrunner recently. Alternator failed on the way to a weekend car show as I pulled into town. Purchased a "rebuilt" alternator from the only auto parts store in town......got me home (90 miles) after the show but was putting out 15.3 - 15.6 volts. Replaced the voltage regulator but no change. Heard from other Mopar owners that the 'rebuilt" alternators are problem prone so order a new Tuff Stuff American Built with American parts alternator and problem is solved. Runs at 13.5 at idle and up to 14.5 when under a "load".
Good luck hope this helps.

 

[furyus]

Have you made sure rhe regulator is grounding to bare metal? Sand the back of the mounting bracket, and the firewall. Also, run a nice sized ground wire from the engine, to the regulator mounting bracket using star washers. These cars are sensitive to good grounds.

 

[Scatransit]

Ignition terminal on regulator to positive post on battery: 0.21 (or -0.21 when leads switched).
As for the alternator case to regulator mounting--if you mean the regulator mounting bracket on the fire wall, it's 0.0.

Electrical systems are not my forte. Between an understanding gap and other life activities, delays occur.

You successfully measured voltage drop. Simply put, voltage drop is the measurement of how much voltage is actually being used up in a given circuit. It is probably the most useful (and least understood) test in the automotive electrical diagnostic world. Measurements close to zero is normal for a healthy circuit. It is measured by putting the DVOM voltage leads in parallel with the circuit being tested while it is "live". Good luck with it!

 

[72RoadrunnerGTX]

Well I guess I jumped the gun a bit here (see my reply to the original posting below).
When I first installed the Tuff Stuff Regulator all I did was start the car and let it run at idle and the voltage regulator was showing just over 12 volts so I thought it was fixed. Well this morning was the first time I had a chance to drive the car and it jumped back up to 15.3 volts when driving Called Tuff Stuff and come to find out that when one purchases a new Tuff Stuff alternator one needs to also purchase a Tuff Stuff Voltage regulator..was told they are made to work together. So I ordered one today and will post the results when I get it installed.

A miss-match in brand names between regulator and alternator shouldn’t make difference in battery charging voltage. The Regulator sets the voltage based on what it senses at the blue wire terminal. I’m running a Tough Stuff 7905 and a MP original style reg. Just as with the mechanical regulated system discussed in this thread, check for excessive voltage drop at the regulator. ’70 and up column mounted ign. switches use Molex connections at the base of the column that, just like bulkhead connectors, tend to build up resistance, overheat and add to voltage drop problems.

 

[70Bronco]

Have you made sure rhe regulator is grounding to bare metal? Sand the back of the mounting bracket, and the firewall. Also, run a nice sized ground wire from the engine, to the regulator mounting bracket using star washers. These cars are sensitive to good grounds.

Yep. It is well-grounded.

 

[joemish]

66 Belvedere II 361. I'm getting 15 volts to the volt gauge, battery, & everywhere else. Installed new volt regulator, it has good ground, and I'm still getting 15 volts. The green wire on the regulator registers 8 volts, everywhere else: 15. Where do I look now? How do I diagnose this?

View attachment 516584

nothing is wrong. If you were below 12 that would be a problem. not all gauges are 1000% accurate. your car is fine.

 

[ExWrench]

66 Belvedere II 361. I'm getting 15 volts to the volt gauge, battery, & everywhere else. Installed new volt regulator, it has good ground, and I'm still getting 15 volts. The green wire on the regulator registers 8 volts, everywhere else: 15. Where do I look now? How do I diagnose this?

View attachment 516584

Have the battery checked, if its sulfated it basically refuses a charge and pushes back with a high volt reading within the veh electrical system. It means the batt holds a light surface charge but cant supply deep cycle cold cranking anymore.

 

[70Bronco]

Follow up time. It is the voltage regulator. Using one of the suggestions mentioned here, you make a mechanical adjustment to the regular itself. The shop manual describes it as follows:
"Adjust upper contact voltage setting as necessary by bending regulator lower spring hanger down to increase voltage, up to decrease voltage settings. Use an insulated tool to bend spring hanger. The regulator must be installed, correctly connected, and retested after each adjustment of lower spring hanger."

It's touchy--easy to bend too much or too little--but bending the hanger does the trick. I still have to fine-tune mine to get the voltage exactly where I want it. When I'm satisfied, I'll post the result.