Why am I getting 22-30 volts?

[GregoYatzee]

Charging issue in my old FrankenFord. My truck is an early 70's box turned into a dump truck. Base is an f350 and cab is 1970 f100 with a 72ish 390 engine with points ignition.

I've found two related wiring schematics. This is the one that matches my wiring... http://www.fordification.com/tech/wi...350_master.jpg (This has the volt gauge rather than light.)

Nothing had been changed the 8+ years I've owned the truck except for replacement of the fuse link when I first bought it. (I haven't driven it more than 100 miles per year.) Early this summer, the truck would die after driven for a bit. My final diagnosis of the problem is charge voltage at 22-30 volts, which caused the wiring to get very hot and blew fuse link. With fuse out, I can remote start truck and it will run, with high voltage (not charging). I separated all fuse link connections with individual blade fuses. The only fuse to blow is the wire from the battery terminal of the alternator. This however doesn't help me understand what is causing the high voltage, I guess is the core of the problem.

The last several months I have been trying to sort this problem. I replaced fuse link with a blade fuse holder and even replaced entire fuse box with blade fuses. No change to problem. All grounding I have tested have tested good. Replaced voltage regulator, same. Tried a spare alternator, same, both bench tested good. Most recently, I replaced distributor, alternator, ignition switch, coil, cap, rotor, plug wires... resistor wire after it burned out from testing... all new.

Further, in the process of trying to eliminate possible bad wiring... removed all radio wiring, cut feed to roof lights, pulled all fuses... disconnected lighting wiring as best as I could track it down...(didn't spend a lot of time in lighting area) Disconnected all remaining switches (wipers cig lighter, etc...)... V regulator has ground wire cleanly bolted to it. I suspected a naked wire short, which is why I've removed all the shade tree radio wiring. The dash harness looked to be fully wrapped and intact (wipe off dust, looked new). I have unwrapped 90% of the wiring harness and there is no sign of damage to any of the wiring. I have traced and tested all related wiring.

The ribbon sheet on back of instrument cluster is melted between voltage gauge lines. I have been testing with cluster removed, my assumption is that removal will not affect circuit. I plan to manually rewire gauges after fixing problem as I don't plan to spend $80-100 for replacement that is also 46 years old. Optimally, I'd like to find, fix the problem and move on. If necessary, I'm willing to wire the charging system with new wire, I have what I'd need. Truck is nearing the end of it's life and I'm not willing to spend a lot of money on it. I already have too much invested to let it die. I have done countless web searches and can find NO results for this voltage range. Everything talks about 16 volts being high. When I have a problem, I have a problem...

[Jacksdad]

Someone else will be able to give you better advice on your charging issue, but I just wanted to say hello, and welcome. Any pics of this beast? F350s are few and far between, but we've got a growing number of them here on Fordification.
from San Diego

[Ranchero50]

What does your battery read with a good digital voltmeter?

22-30V does not compute. Also factory gauge was an ammeter, not a voltmeter (D-C not 0-16vdc)

[GregoYatzee]

Thank you for the welcome.

I keep battery on maintainer, is at 12.6 volts (btw, battery is new last year). I plug meter at fuse holder to wire from alt b to battery... With truck running is where I get the high voltage. The resistor wire quickly gets hot and if I don't shut it down, it eventually dies, which I try to avoid. I only run it a couple minutes at a time.

...and yeah, the 22-30 volt does not compute... I called a local shop and he said there is a small handful of things that could cause this, but this truck is too far gone to spend that kind of money on. I have yet to find that sort of info anywhere else on the planet.

[ThinLizzy13]

Where did you get your voltage regulator? I've had 3 go bad in a row upon install before.

22-30 volts seems awfully high. I saw a thread on a mustang forum where someone was getting 22+ volts. I'll see if I can find the thread again...

[Ranchero50]

Ditto, sounds like the field wire is getting grounded should be the orange at the alternator and regulator. You should be able to unplug the regulator while it's running and the voltage should drop to battery level.

[GregoYatzee]

Got regulator at either oriely or or Autozone. All symptoms exactly as with old one.

I will try unplugging regulator after I get new resistor wire installed. To make sure that I understand... Start truck and pull harness plug from regulator while running? It should continue to run? Assuming so, a good battery voltage reading would indicate a bad voltage regulator?

I appreciate the chatter and help.

[GregoYatzee]

In the attached photo, what kind of connector is indicated. I assume it is a simple splice, but want to ensure they aren't some functional component... such as resistor, filter or anything else I don't know about.

[ThinLizzy13]

Those look like fusible links.

It's very possible the new regulator was bad right out of the box. If you unplug the regulator while running the battery should be at 12v.

[GregoYatzee]

Ditto, sounds like the field wire is getting grounded should be the orange at the alternator and regulator. You should be able to unplug the regulator while it's running and the voltage should drop to battery level.

I tried unplugging vr, the engine died.

I replaced the ground wire from alt to regulator as original had heat damage to shielding.

I did the full-field test from this page: http://www.fordification.com/tech/charging.htm This made voltage increase to 34-40volts... engine did run smoother though.

Now I have no idea what to do.

[BobbyFord]

Time for a 3G swap

[GregoYatzee]

Time for a 3G swap

Isn't that just essentially installing a bigger alternator? There is something causing 3 different alternators to produce insane high voltage. The problem is not the alternator. I guess, basically what you are saying is that I need to rewire the charging system? There is essentially no power demand other than engine, brake lights and turn signals. There is no radio, do not drive at night or in the rain... heck, there isn't even heat. All auxiliary lighting has been disconnected. I don't need the power. I will start working on rewiring the entire charging system and leave everything disconnected as much as possible.

Question... Should I rewire exactly as is, or should I wire it the other way using all four vr wires and the stater in alternator? The ribbon wiring to the ammeter is fried so that could save me the repair there. Bottom line, the cab is in it's last years and I just want to use what's left of it before looking to replace the it. Rust had been repaired long ago and is well beyond repair.

[Ranchero50]

I'll be honest, when reading this thread my eye go crossways. 22-30 volts doesn't make sense. At that voltage you would be cooking batteries and having other serious issues. I don't know what the answer is but you are going to need to dig through your wiring and find what's melted together.

What is your battery voltage across the terminals when shut down overnight and then when running?

[GregoYatzee]

I'll be honest, when reading this thread my eye go crossways. 22-30 volts doesn't make sense. At that voltage you would be cooking batteries and having other serious issues. I don't know what the answer is but you are going to need to dig through your wiring and find what's melted together.

What is your battery voltage across the terminals when shut down overnight and then when running?

Yeah, my eyes have rolled back into my head a few times...(especially when I have hit it on the hood latch...)

The voltage at battery overnight is 12.6 when I have charged it. Right now, it's about 12.4 from my starting it yesterday. The battery has been protected by the fuse. The high voltage reading is from the large gauge wire from alternator to the solenoid.I leave fuse out and start remotely (as ignition switch will not work without this connection.) When running in this state, voltage is high. When I jumper the vr, it goes higher.

The only wire that had ANY damage was the ground from the alternator to vr mount bolt. Replaced that yesterday. I also replaced the resistor wire. There was slight heat marking on it, but it still tested good. All other wiring I have removed from wrapping has been clean, smooth and intact. Every wire I have tested, has tested proper continuity and/or resistance.

I will make and post a vid to youtube today and post it here showing the process I have been using.

[GregoYatzee]

Following is link to my video.

https://youtu.be/oWrlzIJIxig

I will work on isolating the two wires referenced in video.