You could be having some ground bond problems, engine to body, body to battery, etc.

 

I'm not familiar with that brand equipment, but have worked a bit on similar systems. To check everything out, I'd first confirm that the battery was behaving normally, perhaps by disconnecting it and putting a good charger on (one I knew well) after it's been sitting a good while, to see how the charging current and voltage behaved. Then, with battery attached and key on, engine off, see how much current is being drawn from the battery. Maybe unplug the alternator and see if the draw changes much. Speaking of that, what kind/model/output alternator is it?

Do you have a schematic for the (original) charging system?

Is there a significant difference in measured voltage at the battery vs alternator output, while the engine runs?

Wonder what would happen if you inserted a 10w variable resistor in the circuit to the alternator rotor (slip rings, and increased it from zero, while watching the output voltage? Maybe monitor the rotor circuit voltage too, to see if the regulator tried to compensate by raising the volts?

I agree about always checking for good grounds on everything involved.


.

 

I agree that you may be having ground problems because after 1970 Chrysler charging systems the regulator controls
the ground side of the field winding in the alternator.
First the negative cable from the battery should go directly to the engine block.
Then there should be a bonding cable from the engine to the firewall.
Clean all these connections and the mounting points for the regulator of all dirt, grease and rust and apply dielectric grease.
There's no magic bullet, you just have to put in the work.

 

Grounding would be my guess. I would hook a jumper cable from negative terminal on battery to mounting bolts on regulator and see if it changes anything. Next negative post to alternator mounting bolt.

 

The old Dodges grounded the Field on the alternator.................it was all the voltage regulator did.

Sometimes you need to run a jumper from the battery Neg terminal to the body. You can't count on body grounds on old trucks. Any clean spot on the fender will do.(THIS IS NOT A TEST, IT'S JUST A COMMON SOLUTION TO A BAD GROUND...........RUN THE TEST TO VERIFY)

The actual factory test for the system was to temporarily ground Field(regulator disconnected at alternator IIRC), and observe voltage. It should run high.............around 16+. If it didn't go above battery voltage (12-13), it was a bad alternator. The alternators generally failed with an open diode as the culprit. Been years since I worked on one, but this was the test as I remember it. Look up a "Full Field" test to verify. Like I say..............it's been years.

 

A good system will run well above battery voltage. Something close to almost 14 volts, depending on the system. This is why I don't like voltmeters on trucks.........I prefer an ammeter. An ammeter will simply show if the battery is receiving a charge, and accepting it. Bad batteries won't accept a charge.

 

Ok... the grounds were cleaned up last fall when I had ignition probs, but I'll go through them again. I know we added an extra ground right from the battery to the ignition module base and I cleaned the grounds at the regulator when I changed it. I have had ground cables fail internally before... might be time to change out Mr. 1976. Another culprit my Mopar guru suggested was bad diodes in the alternator so we'll go through that too. Taking off out west next week so it might be a couple weeks before I get back to it. Plan A is to put an old regulator on it from another vehicle that was "running when parked" and test out the diodes.

 

Bad diodes, common fault I covered..................easy check..........should only pass current one way. Open diode..............no passeee current neither way.

 

either....................geez

 

Just happened to have a 2012 Kenworth with a Cat engine in today, thing was doing all kinds of crazy stuff, throwing wierd codes and the charging system was part of it. The rest of the electrical system (lights, etc.) were working just fine. Turned out to be a 6 gauge ground wire between the starter and engine block, one terminal at the starter ground was corroded to the point that when I yanked on it, it just pulled apart.
And on Peterbilts the most common ground problem is the wire from the starter ground to the left front cab mount. Makes the gauges and body control module go nuts.

 

But mine was built in 1976... it should know better by now...

 

My old Dodge motorhome was a '76 and quit charging once, It had a broken wire from the field to the reg. I forgot all about that one until a little earlier. Of course i just bought a new regulator first... :angry:

 

Bad diodes will cause low voltage output.
Your diodes are fine.

 

Did you ever resolve this issue?

 

Not entirely... the shop has been tied up with a dismantled tractor waiting on parts and I've been using the truck to move grain around the yard so I can load semi's, most of which haven't showed up yet either. My plan is to run a new wire from the ignition switch to the regulator (bypass the bulkhead connector in case that's part of the problem) and new wire from the regulator to the alternator, and I've got a new more expensive piece of Chinese regulator. If that doesn't cure it, I might follow Dave's lead and go for the single wire. I've got one in stock and I've put them on older JD tractors with good success.

 

I replaced with single wire alternator.

Quick and easy

Dave

The application is a 1976 Dodge grain truck, D 600 with a 360 2 barrel, 5 and 2, but the same regulator was pretty much used on everything Mopar from 1970 until the late 80's. Silly little silver or black box on the firewall with 2 wires attached.

View attachment 1736520

My problem is this. The unit was replaced with the alternator about 2 yrs ago, but this fall it started periodically failing to charge the battery. I put the battery tester on one day last week and it was kicking out 16 volts. When the unit warmed up, it quit charging. I've cleaned cables and since it is capable of putting out 16 volts, I don't think the alternator ( it's a Bosche replacement) is at fault. On Wednesday I replaced the ignition switch ( it was feeling sticky, and supplies the power to the red wire going into the regulator) and the regulator with a new one from Wilson. Right off the hop, as soon as the engine fired at fast idle, it was booting out 16 volts ( or more, that's as high as my tester reads and it was pinned). My 2nd suspect would have been bulkhead connector if it was sending intermittent current to the regulator, but at this point, there was no vibration or movement or anything to trigger sketchy current to the regulator. I backed the truck outside and let it idle down off fast idle and the current relaxed to around 14.5. I kept the meter on while I was unloading the canola in the box, and just sitting at idle, the voltage would vary from 14 to 16 volts... so even brand new, this regulator wasn't controlling voltage as much as idle speed was.

Looking online, I've found comments that the Chinese knockoffs are copies of the original 1970 patent, and that as soon as you put more amperage on the alternators, they fry... often in 2 days. Sounds familiar. I've found an AC Delco version with a 2 yr warranty for $36 Cdn., or an original Mopar unit for $75, but before I throw more money at it, is there anything I may have missed? Is there anything besides a voltage regulator that would cause the charging circuit to over charge? I'm thinking a short should affect amperage, but not voltage, and if I've run it for several hours, anything shorting out would have fried by now. Thoughts? I've also got a single wire Delco alternator in stock I could put on and leave the external regulator off, but I'm not sure if that would affect the ignition brain box.

 

So... I finally got back to the old Dodge and it was pretty much a repeat performance of what 12V described for his motorhome. I bought a new high end regulator, a new plugin for it, and replaced all the wiring to the alternator from the firewall forward. When I was removing the green wire from a clip at the front of the valve cover, it turns out the insulation got brittle from the heat of the manifold, and it as well as the plastic clip that held it in the metal clip on the valve cover had disintegrated. Looked fine from the outside, but the wires were gradually frying away from inside the metal clip. So, the old beast now has a new regulator, all new wiring to the alternator (wrapped in plastic snake to prevent a repeat performance) and a new voltage gauge to keep track of what is going on. Even got a couple LED's added in to help out the high beams. Seems to be working fine now....
View attachment IMG_9162.jpg
View attachment IMG_9161.jpg

 

So... I finally got back to the old Dodge and it was pretty much a repeat performance of what 12V described for his motorhome. I bought a new high end regulator, a new plugin for it, and replaced all the wiring to the alternator from the firewall forward. When I was removing the green wire from a clip at the front of the valve cover, it turns out the insulation got brittle from the heat of the manifold, and it as well as the plastic clip that held it in the metal clip on the valve cover had disintegrated. Looked fine from the outside, but the wires were gradually frying away from inside the metal clip. So, the old beast now has a new regulator, all new wiring to the alternator (wrapped in plastic snake to prevent a repeat performance) and a new voltage gauge to keep track of what is going on. Even got a couple LED's added in to help out the high beams. Seems to be working fine now....
View attachment 1740044
View attachment 1740045

Yeah, I feel stupid about the motorhome thing. In a hurry to get out of town, I just grabbed at a straw. It's funny how I will troubleshoot a customer truck completely before ordering parts but I'll cost myself money I don't need to spend sometimes.

 

[emoji106]


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Well... most of it is getting used for it's intended purpose. One side got absconded for testing equipment... a very old school grain moisture tester, and a very new school soil tester for nutrient levels.
View attachment IMG_9229.jpg

View attachment IMG_9230.JPG

 

lol... yep... finally got used for it's intended purpose...

 

Oh, I'm not sorry I did it. Pretty much everything in the ignition system is new now except the bulkhead connector so I know where to look next time. It's running much better than it was before, now if I get the exhaust leak fixed again and a new muffler, the backfiring should be gone.

 

It's like a science lab [emoji41]


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It is... that latest toy is a shared venture between 5 farms, but it's living here as a central location near a beer fridge...

 

I've also got a single wire Delco alternator in stock I could put on and leave the external regulator off, but I'm not sure if that would affect the ignition brain box.

No interface on trucks that old. Their ignitions are delightfully simple and for some years you could actually swap Ford and Dodge modules and HEI modules by pinout though obviously the Ford and Dodge boxes ain't goin' inside an HEI cap. I saw that in Hot Rod or Car Craft before the internet and they posted schematics. The GM design was the best for simplicity and so good the DUI (Davis Unified Ignition) distributor was designed to mate HEI with Ford engines. I just looked and they make 'em for Mopars (and Cornbinders!) but stock parts are less expensive.

https://performancedistributors.com/product-category/distributors/page/2/

HAMB is a fine old resource. If contemplating a swap I'd ask there.

https://www.jalopyjournal.com/forum/threads/chrysler-ignition-module-swap.190613/

Single wire GM alternators are a dandy design and easy to fix at home if the regulator poots. I'd use any excuse to swap.

 

It could happen yet. I have a feeling that there is sometimes intermittent current getting through the bulkhead connector that messes with the voltage regulator. Thinking the single wire Delco would avoid that...
I used the same nik when I lurked around the HAMB too... haven't been in there much the last few yrs...