I'm entering the realm of First Gen electrical sorcery ...

1991.5 W250
Voltage regulator relay.
Headlight relays.
Original alternator.
Volt gauge worked prior to removing the cluster and repainting the needles but not after. Will have to work on that.

Boiled the battery. Gauge not working and I didn't smell it cause it was a bit chilly and the floor vent was closed. Overcharged for about an hour.

Got a new Voltage regulator (warranty, number three in seven months) and read in the directions to make sure the green wire from the regulator isn't going to ground. So I got the meter and probed the green wire on the regulator plug to the alternator case. Well, it showed continuity.

I got the following readings (all on the ohms X1 scale):
Green at the VR plug to Alt. case .. 4.9 10
Green at the VR plug to upper field screw .. 9.2 1
Green at the VR plug to lower field screw .. 5.2 9

Upper field screw to Alt. case .. 4.8 11
Lower field screw to Alt. case .. 8.1 2
Upper field screw to lower field screw .. 5.1 9

Looking at the wrong scale, correct ohms in Red

Is this enough information to determine anything. I didn't install the new VR, going to wait until I'm comfortable that the alternator is good. I read through the stickies but didn't find anything that led me down the path of knowledge.

Thank you for any help,
BlueW250

 

I would disconnect the green wire from the alt. as well then check to see if it is grounding out. This is just testing that short run of wire between the reg. and alt. with nothing else hooked to it.
I would also double and triple check all grounds- battery to block, battery to fire wall/ chassis, check with ohm meter. Also check how well the reg. is grounded.

 

Well now, That changed some things. Note that I corrected the readings in the OP. Looking at the wrong scale. I used to say I wasn't smart enough to use a digital meter, guess I'm not smart enough to use an analog one either.

With the battery disconnected and the wiring harness removed from the alternator:

Green at plug to Alt. case, upper field screw, lower field screw and grounds .. All no continuity
Ground to grounds, motor, brackets, Neg. cable, Alt. case, VR case, pump, anything grounded I could find .. all show 1 ohm or so.

Upper field screw and lower field screw to Alt. case .. Both no continuity
Lower field screw to upper field screw .. 6 ohms

Alt. output screw to upper or lower field screw .. no continuity
Alt. output screw to case, + on output screw .. 34 ohms
Alt. output screw to case, - on output screw .. no continuity
Alt. output wire lug (on harness & disconnected from Alt.) to Alt. case, + on lug .. 9.5 ohms
Alt. output wire lug (on harness & disconnected from Alt.) to Alt. case, - on lug .. no continuity

How does this look? I'm confused. Does the different readings on the couple where I switched the polarity indicate the diodes are OK?

Thank you,
BlueW250

 

Yep, looks good.
The "resistance" you see in the diodes is actually caused by the forward voltage drop of the diodes. Being a silicon bridge diode array, that voltage would be 1.0 to 1.4 V. If the ohmmeter supplied a test voltage of 0.8V, the reading would be infinity. If the ohmmeter could disregard the voltage drop in the diodes, the resistance would be 0.1 ohm or so.

You can find a shorted diode with an ohmmeter, but you can't readily detect an open diode. It takes an actual spin test to find that. Symptoms of a single open diode would be about 1/2 output at full field and drive.

Resistance readings on the output wire are insignificant. They are caused by non-linear connected loads, clock, computer, radio memory.

 

Thanks to both for the help. I'll put it back together. Regarding the open diode, since it was boiling the battery can I assume that to be somewhat unlikely?

I believe my test drive will include a NAPA visit to locate a temporary volt gauge that I, like Paul-1850, can use as a method of monitoring the voltage regulator until I can get the dash gauge fixed.

Are there any theories as to why these old pickups seem to enjoy burning out voltage regulators. My first one lasted 22 years. Lately the lifespan has been much shorter. I have heard the "Chinese junk" explanation. Another was that the undersized wiring was acceptable when new but with years and corrosion adding up it makes the regulators life harder.

My last two failed regulators had the same rust colored "stain" on the back bottom half inch of the silver housing. It looked as if the black filler plastic has shrunk slightly, water had entered, internal magic stuff had rusted and the rust laden water had oozed out and dried. I added silicone to the new one as a sealer around the edge.

Oh well, off to reassemble. Having a '91 W250 isn't just a job, it's an adventure.

Thank you,
BlueW250

 

I suspect that the same regulator is being used for these 120 amp alternators that was used for the early 40 - 60 amp alternators. While they don't require any more field current, there is much more iron in the field magnetics, which would make the back EMF spike from arcing brushes go to higher voltages.

In the salt water marine world, where an electrical failure could be life threatening, there are regulators that are reliable, albeit not cheap.

Between that and cheap construction, failure rate is high.

 

I swear I read someone had converted to a Ford voltage regulator with good success, but I can't find in in the search.

Anybody remember that?

 

The Ford regulator works better or is more consistent in charging than the Chrysler, it also last a lot longer when used with the cummins alternator. I don't have part numbers but their is a pigtail harness for the Ford regulator that can be wired into the dodge harness.

Their also is a much better version of the dodge regulator but it seems no one anywhere wants to keep them on hand as the are 2-3 times the cost of the standard duty and you know 90% of consumers buy items based on price and not on quality or value. The easiest way to know what your getting besides the price is the actual weight of them as the good one that stand up the best are nearly twice as heavy as the ones from China or homever can make it the cheapest that day.

 

Well, I looked at the marine regulators. There seems to be groupings at $200+, at $99.95 (which used to be the cost of a paint job from Earl Shive), and the bottom end at about $31. Mr. Martin, may I call you J_, Could you offer some insight as to what I'm looking at? I fairly positive these are not going to just "bolt right up" even considering creative wiring techniques.

I also, briefly, tried to find some info on adapting a Ford regulator. There were a couple of old threads on other sites that touched on it but, in my brief search, I found no specifics. I"ll continue looking but if someone finds it could you post where?

One post had an interesting tidbit about the posters installation of an alternator "cut out" switch. His description indicated that when he would see the volt gauge get dangerously high he could flip a switch and the alternator would stop producing charge. This interests me. While this isn't the ideal fix, it would protect the battery from the overcharge to buy time to finish a trip and then proper repairs could be done. Could someone comment on where this switch might be connected? Just for sizing and simplicity I would assume a switch would be best in a control wire rather than the output wire but my understanding of zaps and killiwiggles is quite limited.

The regulator I'm currently smoking every 2 to 3 months is the 2 year warrantied NAPA Eichley (sp). I didn't notice the weight but the price would seem to indicate it's either one of the better ones or produced for the gullible old fat bald guy market.

Thank you,
BlueW250

 

Mopar Performance P4529794, run a dedicated ground from a mounting bolt to the sheetmetal, and be done with it.

 

Advice taken. Ordered this yesterday. Needed a backup anyway and this might be the one.

Already have the dedicated ground as described. Also going to add a ground loop across the top of the engine through sheetmetal, VR mounting bolts, Alternator case, engine block, headlight circuit and battery negative.

Then I'll put the recommended VR behind the seat, run the current NAPA 'till it smokes, replace it with the recommended VR, replace the smoked NAPA under the warranty, put it behind the seat and carry on.

I still am intrigued by the alternator cut out if anyone knows where to install the interrupt switch.

Thank you,
BlueW250