Ok, I've been reading heavily everywhere to diagnose this.

Truck cranks forever & sputters when letting off the key. For the last 6 months it was starting often when letting off the key. I've read about voltage drop through firewall plug and bad ignition switches. I've improved the problem by either replacing or fiddling with ECU harness (converted to Mopar electronic ignition). That fix doesn't last long and it happens again.

I have a Volt meter in place of AMP gauge inside the truck and it is now reading at 10- while idling and getting close to 12 with rev. Previously, it was 11.5 @ idle and almost 14 with rev.

I know there are a lot of variables, but is there a diagram somewhere that shows me acceptable voltage readings to the corresponding point under the hood? I know there is expected drop for each component but trying to figure out what readings I "should" be getting.....

Thank you in advance!

In order to know your voltage drop you have to know what is coming out of hte alternator.

10V at idle with 12V revved up is BAD.

11.5v at idle with 14 revved is also bad.

Since we have no idea where you voltmeter is actually tied into the system it's hard to say what it's reading. If you simply bolted the two ammeter connections together and used that point as the freed for the voltmeter then you should be reading alternator out put and if it's that low you have serious issues.

We may as well start at the beginning ...

What is the reading at the battery positive - (use engine block for ground)

engine off -
engine at idle -
engine at 2500 rpm -

What is the reading at the alternator stud - (use engine block for ground)

engine off -
engine at idle -
engine at 2500 rpm -

What is the reading at the coil positive - (use engine block for ground)

engine off -
engine at idle -
engine at 2500 rpm -

Once we have these we can go from there

Check your Ballast resister.

There really isn't an acceptible amount. Variances of .1 or so are expected.
But it sounds like you aren't charging at all.

It also sounds like you have done some modifications so a generic 68 diagram might not help.

The key is voltage based on the ground.
That is to say, where you are tapping the ground for will affect the voltage you see at whatever line you are checking.
So it matters what the ground is for the item that needs to get the voltage.

So if I test the voltage reg for the charging system, I touch the sensing line(which is exposed on a factory 68 but not on the 71 and up) for the positive and the case of the voltage reg for the ground.

IF the case is not properly grounded the voltage will differ if I used the battery for ground instead.
Both of the actual postive voltage provided and the ground to the voltage reg will change what the voltage reg shows.

All of these readings should be compared to the battery directly using the battery pos and neg posts.

Also be careful on using the bolt or screw holding a wire in place instead of the actual wire as the touch point, as this too can give you a false reading depending on how good the connector is on that wire.

Ignore this.

The ballast resistor will NOT have any affect on system voltage, which is very low.

Nor is it used in START. It is bypassed with the key in START and the fact that it will sometimes start when the key is released shows it is good.

What about the ignition switch? You could have bad or dirty contacts in there that are not allowing you to get a good connection when starting.

Thanks ya'll! I will report back.

I did a clean Madd rewire all the way to gauges so solid wire where amp was. Voltmeter feeding from full volt side of cluster

4 pin orange box I am assuming. I would jump 12V from the battery positive post to the blue yellow ECU terminal and to the coil positive primary terminal & seperately (on the ground side) from the ECU base to ground then crank it & see if it starts several times in a row & only let it run for several seconds if/when it does start to confirm or elim the coil/ECU are good tho they can be OK when cold then act up when hot but you did say this was an initial in the morning starting problem. then as said check voltage drops at the coil/ECU when cranking OR just start cleaning ALL terminals/connections especially the bulkhead & ign sw.

Thanks Robert - hoping you would chime in to reason me through another issue. I'll get you a plane ticket one of these days.

Battery was 12.5 across terminals. I got 11.85 tops at the positive alternator stud but I am idling super low?

I did replace the ignition switch with new for kicks and it started easier twice in a row. Voltage gauge inside still reading low.

I'll get some solid readings tomorrow and report back.

Thank you for the kind words & I could use a vacation but the thought of the airport delays would probably make me want to stay put. for the charging rate I would confirm that the battery is full charged by slo charging it with a charger to full charged then put it on a fast idle & see what you get at the alt & at the batt terminals. I'm wondering if this is a charging rate or a voltage drop (connections/terminals) or a part (coil/ECU/switch) issue. The battery could be sulphated (least likely) but a possible potential. We're getting there.

Wally,
As FastBob states above, check your bulkhead connections. Your comment "sputters when letting of the key" is a classic indicator that the STARTING circuit to the ignition has failed. Not uncommon.

If It wont fire until the key is released the blue/yellow circuit to the ECU is dead during crank. Where? It depends if how it was wired when installed. Where was the wire attached to the ignition on circuit? Be aware that Mopar has 2 ignition circuits. Ignition 1, is hot in run but not crank (I believe red on your truck). Ignition 2 is hot in crank, but not run (I believe pink on your truck). The best way to find voltage drop? Connect a voltmeter hot to hot (positive side drop) or ground to ground (negative side drop). In your case battery positive post to the Blue/yellow wire. Crank the engine. By all rights the voltmeter should read zero. It won't. What ever reading you see is how much voltage is lost between the circuit testing point and the battery positive post. Don't be surprised to see readings of .5-1.0 volts. More than that is an issue. Start at the battery terminal and work your way down the the circuit. Do this test while the circuit is loaded. Such as while cranking, while running or with what ever component you want to test is switched on.
Doug

Ok report #1

Battery fully charged

Voltage

Batt positive
engine off 12.68
650 rpm idle 12.26
2500 rpm 15.5

Alt stud
Engine off 12.67
650 idle 12.25
2500 rpm 15.5

Coil positive
Engine off 0.03
650 idle 10.3
2500 rpm 11.6

that 15.5 is too high.
what did your voltage reg read at the sensing line?

As Andrew said, 15.5 is probably too high, your idle is too low. Your coil voltages look ok and where you have checked I do not see a voltage drop issue.

I would say voltage drop to the voltage regulator on the sense side needs looked at, usually it's a blue wire but it is the switched 12V feed to the VR. Measure that to engine block and it should be the same as the battery + terminal or alternator output stud voltages, if not you have an issue if so it's probably the regulator.

In 68 you should still have the single field terminal alternator with the mechanical regulator system, unless it has been changed.

If you are still running the mechanical voltage regulator instead of the later electronic version of it (not to be confused with the 70 and up regulator) you can adjust turn on and turn off voltages. To tell if it's the mechanical regulator look at the bottom, if it has a couple wire wound resistors it's the mechanical one. The FSM has adjusting procedures in it.

No truck FSM's, but the 68/69 pass car ones have the relevant info in them

http://www.mymopar.com/index.php?pid=109

I would think about converting to the newer charging system

http://www.mymopar.com/index.php?pid=78

I have not probed the regulator points. I did swap the regulator for no change. I then decided to swap another alternator in. That changed the volt ratings inside the truck and it now pulses by a half an amp or so..

See my youtube upload https://youtu.be/6DkWHOLzsxk

that is what a mechanical regulator looks like when it's doing it's thing.

you still need to verify sensing voltage, and as said before use the case as your ground point.

I expect you will find at least 1 volt drop causing your higher charging voltage.

Actually, i have it set up to newer square back with mopar electronic ign

Are you thinking i should leave it and see how it goes?

My analyzer ws flashing bad alt brushes on the previous alt...

If you have the newer setup and it's doing that you have a problem.

that charging rate is too high. I'm thinking this 2nd electromechanical reg is the problem, a considerably way less 2nd choice would be the alt. I would certainly want to get an electronic reg which most parts house types are now (have no wire wound resistors on the bottom side of it) & a Wells 706 (iirc) was the last electronic one I got but it dont look OE (if that is critical). For sure the starting issue ain't a lack of voltage but it is critical to get this dealt with first as that high of voltage will fry (or significantly shorten the life) of bulbs and any electrical component that is "on" while it is charging that high. As said jump from the batt positive post to the "ign" terminal on the reg but your (posted) voltage drops are about as perfect as I have ever seen & a voltage drop might not be the issue (easy/free to check). I'm assuming the reg is grounded well since it has been changed & confirm the block is grounded well to the firewall/batt neg post. Backing up a bit I'm assuming you have a 2 field terminal alt with one terminal grounded.

Hey Robert - i will post the 2nd alternator results

If you watch the youtube video, that is after the alternator change which was the only thing that affected the reading change at the cab gauge...

I have the newer style triangle plug regulator with both alt wires correctly connected. The hard start may have been a coincidence and is so far cured with the new ign switch. All firewall/harness connections clean and tight...

You know I was out jogging today & it crossed my mind that the unsteady ammeter needle would be from an electromechanical reg that ain't quite right or alt brushes/commutator (intermittent contact) but with your electronic reg that elims that. So I am thinking the alt if your idle speed is up high enough where it is supposed to be. On the high charging rate (which has to be dealt with) a sulphated battery would be the last potential but do continue to check voltage drops & jumping 12V to the reg "side" blue wire terminal would be my first step (a thin pin to stick in the triangle connector).

Will do

That Amp label is stuck over a volt gauge so that needle wiggle is pulsing from 12-12.5 and then on rev it goes up a half volt or so with the same range wiggle....

I'll try to get time this week again. I've never used a volt gauge before this truck so I am not sure how they should be reading when tapping the full voltage at the gauges before the limiter.....

If that is actually a voltmeter then that wiggle/slight raise you reported is normal. but 15+ is still a critical problem.

Gotcha. I'll reflect the recent alt change voltage numbers. I think I switched this alt out originally because I didn't like that "wiggle"

so, maybe I've been running a jacked up alt for a while and it took more of a dive recently.......

Ugh. Baffled by high alt stud voltage reading. Had a new alternator on the bench so i swapped that in. New battery because the old was not holding charge. All of my voltage readings are very similar to first numbers posted (15.6 at alt stud)

Tried a new regulator for kicks with no change. Figured it was worth a try...

Alt wire goes straight to starter relay (madd style) could it be something in that neighborhood? Fusible link connections?

Starting problem cured with new switch. Volt gauge still pulses 12-13 volts

Do you know how the IVR works? It's a clicker type regulator that uses the current passing thru it to heat up a bimetallic trip that cycles the load (gauges) on and off, you pick a poor source for your voltmeter as it is seeing that load clicking on and off.

Did you ever get a reading at the voltage regulator sense voltage? I didn't see it in the thread. I suspect it is low.

I'll take that reading over the weekend.

Hey Supercuda - the gauge is connected to voltage once Key turns on. a separate wire feeds the limiter to the gauges. Before the hard start and low reading issue, the gauge read steady - but I admit that I never checked the voltage when I thought the system was operating correctly.

The needle never pulsed before this whole issue..... When I fist did the wiring, I had the needle pulse and swapped alternators. Now I wonder if there was an issue with the swapped in alt......

I'll check my connections at the starter relay this weekend and get the volt reading from the regulator. I would think I can check those readings at the field terminals on the alt since the wires connect?

You really want to check as close as possible to the VR. The sense line splits at the ballast so you would not be checking the feed to the VR at all.

If you followed Chrysler color codes the blue wire is the sense line, should be the same as the battery or alternator output voltage. The green line controls the alternator and you need to check each end and compare as that reading will vary depending on load.

Do you still have the factory amp gauge?If it has one try disconnecting it.I had lots of problems with the ones in my trucks.Unhooked all and used a vot meter.That and Wells isnt the best brand for electronics.i use Standards etc.Rocky

Read the thread

Ok, with the vr triangular plug at the bottom of the vr, i got the following readings:

Idle: top wire = 14.4 bottom right = 4.6
rev: top wire = 15.5 bottom right =13

Truck was wired without issue for a few years.

I did question myself after seeing a diagram that showed the ignition feeding from the lower vr terminal. Mine is fed from the top like other diagrams. I used jumpers to swap the field connections onnthe vr for a few minutes. I must have cooked that new vr because after that the alt stud readings held steady around 12.26 and the gauge in the truck was no longer reading.

So far i have not run seperate witing like Robert suggested as i wanted to report back first. In addition, i added an extra ground and cleaned the alt connections at starter relay. New positive bat cable since i had one.

I had a overcharging problem and it was a melted blue wire in my dash harness. It looked like the wire had been pinched and finally over time grounded and melted.

Looks like the voltage sense is reading properly.

What does the ground for both the regulator and alternator look like? I'd run extra for testing.

I had an overcharging and starting problem with my 71 Challenger. Once in a while it would not start. A few times I ended up "pop starting" it. The voltage was low at idle and way over when revving. I'd blow the caps off the battery. I couldn't find the problem and had 3 different garages hunt for the problem. No one found anything. One day I was under the dash and just happened to notice the connector plug for the steering column to the dash harness had a black streak in it. It was the heavy red wire. I clipped the wire on both sides of the connector and bypassed it with a separate connection. It was fixed. No more problems with it not starting and overcharging.

So look for a bad connection. Especially in your hot wire from your starter to the relay.

Thanks - still trying to get some time to bypass some wires as suggested by Robert - banging my head against wall at the moment...

when the shop tested the alt did they give you a sheet with the voltage? which is what it produces when full fielded. You might try this: pull both female terminals off of the alt male field terminals & jump one terminal to the nearby alt case (ground) then hook the voltmeter to the alt (batt stud/nearby alt case) & idle it at a good fast idle & jump 12V to the other alt male field terminal for several seconds, just long enough to see what the voltmeter reads & have all lights/accessories OFF for this. Is this the same 15+V reading you are dealing with? You might also grab a coil of wire & some alligator clips from the HELP section at your parts house & make some jumpers & pull both field leads from the alt & pull the triangle reg connector & jump 12V to the top reg nub and 12V to either male alt field terminal then connect the other reg (side) nub only to the other alt male field terminal & jumper from the reg case to ground & start it & at a fast idle see what the voltmeter AT the alt reads. this takes the wiring out of the picture & only leaves the reg or the alt. & electronic regs almost always either go open (no charging) or full field (max voltage the alt can produce).

Thanks for not getting frustrated with this long lasting Help thread guys. I'll try to see if I have the alt card somewhere. I plan on getting back to this over the weekend. It's super cold out and our 140 yr old house requires attention at times....

Robert/Supercuda - thank you for hanging in there with me. After 20 years of driving old mopars, i always figure "won't happen to me"

I believe my main problem was a firewall connection. When i rewired, i traced back to find that i had created a connection for the ignition feed before it entered the cab. That short portion of the engine harness wire was brittle.

I drilled that wire out of the plug as well as the amp heavy wire and made a tight bullet connection wire to wire after pulling through firewall. I still want to be able to pull everything apart if need be.

In addition, i cleaned my fuse block connections again.

Those fixes now give me 14.7 idle up to 14.5 on the alt stud and a steady 12 on the volt gauge with no fluctuation.

I think i've been overcharging for a couple years without realizing until i killed the last battery.

I am over the moon!!

Excellent

That was too easy!

Happy New Year everyone. My charging issue has crept up again. Here is what I’ve done:

Truck was basically idle for a year or so with engine/trans build. Recently installed with good body grounds. Connections at firewall clean & snug. Fuse block cleaned. Truck runs well and would not notice this issue until 5 mins of driving or so.

Issue with previous charts as guide. I am trying to determine if this points to a particular component. Battery load tested well at a reputable battery shop. Squareback alternator with new style voltage regulator (triangular plug).

Readings (location, Idle voltage, 2500 rpm, engine off)

Battery positive terminal (12.16, 14.7, 12.53)
Alternator stud (12.23, 19+, 12.53)
Coil (10.36, 15+, 0)
Top/center electronic VR terminal (11.27, 16+, 0)

+ sign means it was still climbing

Gauge, key switch and fuse block connections all clean & tight....

Greatly appreciate a bit of input.

sensing line is off 1 volt at least.
how did you check that voltage. or rather what did you use as ground?
you need to use the case of the vr as ground and verify if it is off even more.
It could be a bad ground to the VR, or it could be the sensing line is dropping voltage through the bulkhead connector.

Typically I just run a relay using the sensing line as the key on trigger and a new line from the battery to the vr through the relay.
Or you can find where the bad connector is and clean it up.

You might make up some jumper wires with alligator clips & jump each/all connections including grounds ALL BACK TO THE BATTERY & if normal then all the hard components are good & it is a positive or negative wiring/connector/ground issue. you might remove one at a time till the issue flares which pinpoints the problem. you might have to modify this procedure to suit but you get the jist of it. we gotta do some elimination. stay in touch (we got your back).

Greatly appreciated Robert!. I’ll report back.

Robert, when I jump, should I get a multimeter reading at the gauge each time? And I presume jumping coil/regulator?

we're dealing with a charging issue so we will work on the charging components. jump from batt positive terminal to the top (blue wire) terminal on the reg (stick a thick pin/wire in to get continuity). jump from batt neg post to the reg case. pull the 2 wires off of the alt field terminals (dont let em touch ground). jump from one male alt field terminal to the battery positive terminal. jump the other alt field male terminal to the green wire in the reg connector (use a thick pin/wire). jump from the battery positive terminal to the large alt threaded stud. jump from the batt negative post to the alt case (you might use your jumper cables for this if they are secured good or have a helper hold them). fire it up to a fast idle & see what voltage you get at the battery. only have it running for a few seconds 10 or so (long enough to get a reading) as full fielding from a bad component/grounded wire will fry things in short order. have all lights/radio etc off. I dont think I missed anything. this elims everything except the alt/reg/battery. EDIT we could jump one at a time but that is too much full fielding. you might pull the alt brushes & a visual there, they are a frequent culprit. my gut says alt or reg

For The Life Of Mary. are you guys doing. It is simple logic here. Back probe your connections as the condition is occurring and you will easily diagnose the problem.

he shows the readings clearly show sensing voltage to the VR doesn't match battery voltage, ever. And it gets worse as the voltage gets higher.
If it doesn't match it over charges.

It is just a question of why doesn't it match.
I don't think the jumpers are necessary to prove that. But I think when you are done, jumping the sensing line and vr case to battery power that it doesn't over charge.

Thanks Robert and all. I haven’t heard the back probe term in all of my years btw... keep ya posted.

1 Detail that I want to add that may help. I can drive for 5 minutes without voltage overcharge. Then it will spike up for a few seconds and settle down. I would jump straight to the regulator assumption, except it comes back. My experience with bad regulators is they go and do not regulate again.

I'll get some time to go back over the grounds and respond then. Just wanted to throw that info out there.

Agreed I have never known an electronic reg to go back & forth. I'm thinking a connector or ground is losing/regaining continuity OR the brush assy in the alt is doing the same thing. Keep after it & keep us posted

have you had the brushes out and closely examined the isolated brush holder ?
what does the armature look like ?
also, are the male connections to the brushes clean and tight ?

Have you tried remove the alt and spin by hand to check some friction, contact or weird feeling when spinning? May have not necessary remove the alt but just loose the belts and feel it.

I had once my alt giving up to 18volts at iddle ( more giving RPMs ) but no charge on ammeter ( some charge when giving RPMs ). One of the stator lead to diodes was making contact with just one of cooling vanes on rotor when spinning. Hard to feel but I was able to feel a small "stop" similar to the elect distributor stop due the magnet with reluctor points when spinning. Dissasembled, bent the wire a bit and done.

Good points all! I'm wallpapering this week, but will get back to it this Weekend.

Sorry if its been mentioned but 30 years ago I rebuilt an alternator for a friend and I over greased that bushing in the rear which slung grease out and ended up making a path to ground for one of the brushes and simulated what the voltage regulator does, caused it to overcharge bad

I appreciate everyone's help here. At the moment, I have a tentative fix (until I drive it more).

I double checked connections and grounds and did not find an issue. I kept thinking it was mechanical, because it would run fine for 5 minutes and almost switch to the high voltage. That told me it wasn't a connection.

I cleaned my Alt brushes and at the same time I replaced the VR. I am back to my original 14.7 idle to 14.5 readings at the gauge & across terminals/alternator, so I am hopeful that it was mainly the VR since the brushed looked fine to the eye. Keep ya'll posted (again)!

I have yet to jump anything, but I have that well documented in case this happens again.......

what you might do if interested is unplug the reg & plug it into the old reg & ground the reg body with a jumper & see if it was the reg or the brushes

Hey thanks Robert! After a good few miles, still good. I have never had one fail and act like that which had me chasing. I really appreciate the help and notes! Happy St Patrick's Day!