Alternator Diagnostics

[Vogue75]

So to piggy back off my solar thread, the Crux of the issue with my starting battery has been a less than stellar charging job by my alternator. When the problem crept up I measure the battery posts while running and got 13v at idle and 13.6 when revving. I know this isn't good enough to power accessories and charge batteries but I have a feeling it's not the alternator itself causing the issue. So I went to Dave Place and started running the diagnostic steps for the 3 wire alternator on my 440.


Well I only got as far as the first step because when I measured the ballast resistor with the key on I had voltage drop on the first test. I went to the alternator itself and measured at the posts on the back and likewise had a voltage drop of pretty much an entire volt. The wiring is old and I had thought to rebuild the harness bit by bit, but we are out on the road (although not going great distances so I can move it without the battery dying as long as solar charges it back up, not the best!).


So my question is: Am I correct that the likely culprit is the battery cable itself? I am unable to crawl under the rig until tomorrow in the daylight so I'm trying to get a plan together for when I get down there. The voltage regulator looks old but I understand they're pretty simple and don't die, plus I seem to have isolated the voltages drop to the part of the system before the alternator. According to the diagnostics I plan to be looking for a fusible link at the starter solenoid and testing the cables from battery to alternator. Perhaps it's something loose which would be nice and cheap!


Thanks in advance for any thoughts, that step by step diagnostic has been great.


Edit: I should add my rig has MSD ignition and a Howell TBI (holley throttle body) so there's extra wiring here and there and some connections I could redo for strength.

[Rickf1985]

First and foremost check all of your battery connections bot at the posts and where the grounds connect to the frame. Take them all off and clean them. Check the ground cable from the engine block to the frame, this is overlooked a lot and sometimes it is even missing or broken. Especially on vehicles that have had major engine work.  Any wires that have had the insulation compromised by poking probes into it are suspect since moisture will get in those holes and corrode the wire inside. That will build up resistance.  the easiest way to find a bad wire is to do a voltage drop test from the battery to the end of each wire. If the battery is reading 12.5 volts and then you put your meter ground wire on the battery ground post and check the other end of a suspect wire and it reads 12 volts you have a .5 volt drop on that wire.

[Vogue75]

This was my plan for today. Start at battery and check for drop at every connection until I get to alternator or find the drop. I've worked on cars a lot in the past but this rig is a whole new beast, there's probably 4-5 lengths of wire between the battery and alternator due to these solenoids and switches everywhere. Slightly more complex but basically the same principals. Thanks! I really should start redoing the wiring little at a time but it will suffice to fix this issue for now.


I did replace some of the battery cables in the battery bay, but I didn't do the lengths to the alternator. The battery ground cable is new and I took the grinder to the ground point so it's nice and clean.


Where would I find the main engine ground strap? I'll look when I'm under there.

[Vogue75]

Well good news ( I think) when I went from battery positive I had good voltage through the solenoid in the battery compartment but when I got to the starter relay I had a serious drop. I have two battery gauge wires connected to the same pole on the relay, one goes to the battery compartment solenoid and the other goes to the starter. I've been using a push button start bc the key doesn't crank the engine all the time. Could it be as simple as this short length of wire between the solenoid and the starter relay? I'm doubting myself but a cable is an easy cheap fix and it can't hurt to just swap it out.

[Rickf1985]

If the cable tests bad then replace it if for no reason that it is a bad cable. I do not think that is the charging problem unless the field wire for the alternator is coming off of the reduced voltage side of that wire. You might want to diagnose the starting issue just to be sure you don't have a burnt wire somewhere that is going to start a fire. Try starting it with the key in neutral and see if that works better. If it does then the problem is the neutral safety switch. I am not going to advocate bypassing the safety switch but instead of running extra battery cables you could just run one 14 gauge wire from power through a starter button on the dash and down to the original wire on the starter. Take the original wire off and use only the button but be aware that it will start in gear.

[Vogue75]

Yeah I added a push button as described to make it easier to startup, I though the issue was a neutral safety switch problem so I bypassed it for now.


I may have found a wrinkle now though, it appears the alternator charging cable also goes into the starter relay area, I have to climb back under when I get home but it appears the PO did some kind of bypass where the alternator cable jumpers accross the starter relay. Unusual but definitely could be a source of the issue also.


I understand the pole on the starter relay can serve as a positive battery pole to branch off. If as I suspect the battery positive jumps to the starter AND to the alternator charging cable at that spot (where the voltage drop is present) it could be all related. My next plan is to replace the cable from battery to starter relay and from starter relay to starter.

[DaveVA78Chieftain]

B+ (6RE) from the Battery, Starter cable (6RE), AND the fusible link that connects to the wire (A20) that goes to the B+ terminal on the alternator ALL connect to the "B" terminal on the starter relay.

Voltage at alternator B+ should be within 0.5VDC of Battery B+ with ignition OFF.

Fusible Links (a smaller wire diameter than the wire it is protecting; e.g. A20 is 10 gauge, fusible link is 12 gauge) have a bad habit of degrading with age do to heat resulting in higher voltage loss.

System RUN Voltage (11.5 to 15 VDC) in initial TS steps measured at ballast resistor is used as a convenient location to measure the central system distribution circuit (J10 wire).  All the J10 wires are soldered together in a bundle that is located by the Tranny Dip Stick tube.  The J10 wire is the "sense" wire feed to the regulator.




BTW - little known factos: The Dodge amp gauge on rigs with the round gauge cluster (1974 and later) is actually a milli-voltmeter that measures the voltage across a wire section shunt of the A20 wire going to the B+ alternator connection. Wires A1-18BK (hint hint: A1 circuit; 18 gauge wire; Black wire) and A1-18RE (hint hint: A1 circuit; 18 gauge wire; Red wire).  Amp gauge on 73 and earlier rigs with rectangular gauge panel had the shunt built into the gauge itself.

[Rickf1985]

And there you have it! I was hoping the Dodge Guru Dave would jump in on this one.  I am not really a big Mopar fan unless it has spark plugs going into the valve covers.

[Vogue75]

Ahh yes amazing post thank you! I think we are getting there. So if I measure a full volt of loss at ballast resistor, this is part of the J10 circuit that comes downstream of alternator, since I did my cable tests and found a voltage loss upstream of the alternator and fusible link it's probable that the cable from the battery (both 6REs) is the culprit, or at least one of the culprits if there's more than one? You guys rock that schematic is just what I needed.


I have a voltmeter on the dash but no ammeter, the display isn't super accurate so I planned to wire in a newer one and attach it to the same switch at some point. Edit: It just occurred to me that the voltmeter inaccuracy is probably related to this same voltage drop, and the malfunctioning of the "sense wire" in J10 that's supposed to regulate the voltage from the alternator.

This gremlins time is short! (IMO)

[DaveVA78Chieftain]

Ammeter is part of stock Dodge cluster, not a Winnebago add on. 


On second half of that diagram you will see that you also have additional connections (e.g. ignition switch, half moon connector at base of steering wheel, etc.) in the circuits where losses can happen.  The half moon connector is known for bad connections due to excessive current flow.

[Vogue75]

Okay, after looking at this second page it looks like J10 actually comes from the fuse box which is fed by A20 after the fusible Link. So I'm gonna hope that replacing 6RE wires solves the problem or I'm gonna have to chase around the wiring harness and fuse box (if the link itself isn't bad).

[TerryH]

And there you have it! I was hoping the Dodge Guru Dave would jump in on this one.  I am not really a big Mopar fan unless it has spark plugs going into the valve covers.

Good one!!

[Vogue75]

And there you have it! I was hoping the Dodge Guru Dave would jump in on this one.  I am not really a big Mopar fan unless it has spark plugs going into the valve covers.

Lol this is my first Mopar, Iââ,¬â,,¢m actually enjoying it since most of these parts are readily available. I learned cars on old BMWs so itââ,¬â,,¢s a nice change.

[DaveVA78Chieftain]

Nope, J10 comes from the Ignition Switch (referred to as Ignition 1 at the Ign Sw) and is the "RUN" wire.  The J9 Circuit (referred to as Ignition 2 at Ign Sw) is used to bypass the Ballast resistor and apply a full 12VDC to the coil during start.  Voltage to coil is reduced by the Ballast resistor when engine is running.
J18 is the start signal wire to the Starter Solenoid.

The J10 lead going to fuse box (T/Sig Brk Wrn 20 amp fuse) is power source for the Turn Signal and Brake Warning light.

[Vogue75]

Hmmm perhaps the ignition switch is the culprit after all? I have to do more testing but I replaced the 2RE wires and still have the charging issue. Unfortunately I also moved the rig and now I seem to have a no spark condition after messing around down there and driving it for a bit. Cranks strong but very little power to coil. I'm leaning toward the ignition switch since you mentioned it can be prone to failure and it looks intimately involved where it feeds the ballast resistor and then the coil.


Edit: Welp I just turned the key to IGN 2 (crank position) and pushed the push button at the same time and it sputtered a little bit instead of just cranking (weak spark maybe?). That seems helpful. Previously it was starting fine in position one with the push button, fired up every time. I wonder what I changed? Or it.s an intermittent connection somewhere, maybe at the fusible link if it's failing.


Peeking under the dash the ignition switch looks like it was already replaced, looks like the newest thing under there, and tied with a Chrysler wrap (dealer work?).


I found a post with some tests that can be done at the "half moon connector" so I'll add those to the list too.

[Rickf1985]

I think you need to temporarily take your push button start wiring out of the loop and work with only the factory wiring. You have to much extra going on there that could be adding to the problem. Get rid of any extras even if only temporary. You may find out that once it is all straightened out it will start fine with the key.

[Vogue75]

The push button I've been using now is a temp clip on style one, I've already removed the one I installed in the dash for that reason, but I agree. I think the key will work when I get this all straightened out. There's clearly voltage drop through through the ign switch I just need to figure if it's before the switch or after and where it happens in the system. I'm getting my head around all this wiring it's a damn rats nest back there compared to cars I've worked on LOl

[Rickf1985]

I noticed you were referencing the ballast resistor a lot in one of your posts, Make sure you are checking the voltage on the supply side of that resistor because on the other side in the run position the voltage is substantially reduced and that could be confusing you. The only time you will get battery voltage to the coil is during cranking.

[DaveVA78Chieftain]

Some stuff from my secret stash:

If you want to know most all there is to know about the Dodge Charging system used in that era, then read
Chrysler's Master Technicians Service Conference on Diagnosing the Charging System (March, 1969).

If you want to know most all there is to know about the Dodge Electronic Ignition system used in that era then read Chrysler's 1973 Master Technicians Service Conference on Diagnosing the Electronic Ignition (November, 1973).

[Vogue75]

I noticed you were referencing the ballast resistor a lot in one of your posts, Make sure you are checking the voltage on the supply side of that resistor because on the other side in the run position the voltage is substantially reduced and that could be confusing you. The only time you will get battery voltage to the coil is during cranking.

Yeah I've been been learning more and more. You guys rock thanks for all the help! Iââ,¬â,,¢m certain I will figure it out.

Some stuff from my secret stash:

If you want to know most all there is to know about the Dodge Charging system used in that era, then read
Chrysler's Master Technicians Service Conference on Diagnosing the Charging System (March, 1969).

If you want to know most all there is to know about the Dodge Electronic Ignition system used in that era then read Chrysler's 1973 Master Technicians Service Conference on Diagnosing the Electronic Ignition (November, 1973).

Haha the legend! Thank you! I'm a nerd at heart and self taught tinkerer so I will devour this stuff.

[Vogue75]

Nope, J10 comes from the Ignition Switch (referred to as Ignition 1 at the Ign Sw) and is the "RUN" wire.  The J9 Circuit (referred to as Ignition 2 at Ign Sw) is used to bypass the Ballast resistor and apply a full 12VDC to the coil during start.  Voltage to coil is reduced by the Ballast resistor when engine is running.
J18 is the start signal wire to the Starter Solenoid.

The J10 lead going to fuse box (T/Sig Brk Wrn 20 amp fuse) is power source for the Turn Signal and Brake Warning light.

Is the J10 for the brake warning and turn signal still part of the run signal? I think this wire is where my no start problem resides unfortunately and it looks like a very involved bit of the harness.


With the 6RE cables replaced I get battery voltage in the field circuit and at the alternator charging cable but now when i turn the key on the current isnt getting to the brake light or turn signal lights which usually illuminate at crank for a second. I also cleaned the ballast resistor connectors.

[Rickf1985]

Did you get your 14 RE wire hooked up at the starter relay and is the A20 circuit good at the fuse box? Is the plug between the 14 RE fusible link and the A20 wire good?

[DaveVA78Chieftain]

Main power to Ignition switch and Alternator is shown in red.  For 73 - 74 Dodge chassis (Dodge VIN plate) main power was routed through half moon connector.  Due to failures of the half moon connector, that was changed in the 1975 to bypass the half moon connector.  It would be to your benefit to also jumper the main power lead around that connector also.

The J10 circuit is shown in green.  As you can see, being the primary power ON circuit, it goes all over the place.






The Brake Warning switch provides a ground for the Brake Warning light (front to rear hydraulic system pressure differential detector)

[Vogue75]

Well I got it running again by making a new fusible link and installing it on the starter relay, but unfortunately the charging problem remains. The good news is I can drive it around on the battery and it wonââ,¬â,,¢t get towed and we can keep taking the follow car on day trips.


The other good news is all this stuff was old and brittle so it needed replaced anyway and now a bunch of these wires are new and I understand whatââ,¬â,,¢s going on better.


Now that some of the parts of the system that were apparently intermittent are ruled out Iââ,¬â,,¢m gonna do the basic tests again tomorrow on the charging system with a better understanding and Iââ,¬â,,¢ll report back.

[Vogue75]

I wanted to bump this thread because I finally fixed the charging problem which turned out to be faulty voltage regulator or wiring harness to the regulator. I replaced the alternator with an upgraded single wire power master and the rig is running and charging perfectly. Hope this helps someone!