krautrock,
If the alternator output goes to the battery directly, then the ammeter is no longer being used.
For an ammeter to work it need to either be directly in the battery charge wire, or in parallel to the battery charge.
If the meter is in parallel, its an externally shunted ammeter. Chrysler was using external shunted ammeters in a-bodies by '76. Earlier in some of the other car lines. Trucks I don't know.

Whichever type ogf ammeter was added, the question is why was 40 amps going to the battery?
Or was there anything else hooked to the battery?

This is the one disadvantage of having a voltmeter but no ammeter. The Voltmeter can only indicate whether the regulator and alternator are working. It can not show whether how much charging or discharging is occuring.

This is a slightly cleaned up version of the '74 Motorhome diagram made by Dave78chieftan (linked earlier in this thread)

It shows an ammeter with remote shunt. The shunt is the wire marked A20A - 10 Black
From each end of that shunt wire, 18 gage wires go to the ammeter.
(What he called a 'main' junction is not the same as the main splice we normally discuss where battery and alternator power wires join with the distribution wires.. His is just a junction on the run circuit.

thanks for posting this diagram. looked at a wiring schematic just now.
seems i need to modify my wiring some.
right now the alt output goes to the b+ on the relay, then i have a 10g wire that goes from the b+ to the A20A-10BK inside the cab, there is a splice somewhere in there that goes to the headlights and something else, then it goes to the ammeter. Then, the other side of the ammeter is original so it is the same as the S1-10-RE in the diagram, so it goes back to the B+ on the starter relay. both connections being at the B+ on the starter relay is going to cause it to be inaccurate right?

I started my truck this morning to have a look at the gauge once again, the starter makes the gauge show 15a discharge, then at a slightly high idle it shows about zero, if i rev it up some, it shows a few amps on the charge side.
Like i said before, at a low idle, voltage at the battery was about 12.8v and if I revved it up some it was about 13.3v.

It sounds like your truck's ammeter has an internal shunt.
Because it sounds like it originally had a heavy wire from the fusible link all the way to the ammeter, and a heavy wire from alternator output to a splice or splices with a brank to the other side of the ammeter.
A remote shunt would have small 18 or 20 gage wires going to the meter.

Using that diagram is probably not the best if the rig had an internally shunted ammeter.
From what you've described maybe something like the first one below.
The second one is typical '73 car. I dont have truck diagrams so can't help with that. That motorhome one the guy drew is the only thing I've seen.

15 amps discharge while starting is huge.
The question is why is any current going through the ammeter when you have it wired this way.
As far as the voltage goes, its not very informative. Could be anything from blown diodes to a short sucking power from the alternator.
I think you're best off wiring it up like the factory (using new connectorsand a grommet instead of going through the melted ones).
Then hunt for shorts with battery discnnected, or live, using a circuit breaker where the fusible link(s) goes.

I have reading a bit more this thread. So far so good I can say:

@jcruse64 you don't need to remove the existant wires from bulkhead if they are in good conditions! You can help them with a parallel wiring. That's why I meant a parallel wiring toward to reinforce the existant one. If they were burnt and you were not interested on reinforce it, well remove could be ONE way to make it. HOWEVER I like the idea about keeping it, why?:

Ok, note the diagram! On a standard setup the main splice on cab side gets tipically a 12 wire running to bulhead and one wire running to ammeter. When you install a paralel wire, the stock wire will be still feeding the splice from alt wire, and the parallel will feed the splice from the ammeter side wiring. So your are feeding the splice on two 12 wires ( no matter the gauge of the wire of the parallel path, just talking about both wires arriving to splice )

If you remove the wire from bulkhead you are limiting the splice to be feeded from just one 12 wire, the one coming from the ammeter side. The only way to make this better is feed the splice straight from the parallel path, and replace the wire between amm and splice with a similar one, instead make it easy just using the amm stud as a juntion and keeping the stock one. This becomes on a deeper modification, going straight to the splice. Is not hard, but reach that?

The extra thickness on the parallel path will help on a more efficient charging process when needed supplying the load to the batt throught the amm if was required.

Next... wiring must be matched to the nominal load the car will be sucking as a constant and able to support some peaks INCLUDING the batt load recharging process. IMHO THIS WAS NEVER CONSIDERED by Chrysler same as the real alternator capacity required to a balanced electrical system.

You were asking about what's the wiring gauge required for the upgrade? Keeping the stock 12 gauge one 10 gauge is more than enough. I used 8 on my car for the parallel path just because I had that wire on hands, but could use very well 10. Use 8 won't hurt anyway.

my truck is wired like this now.
[img]https://board.moparts.org/ubbthreads/ubbthreads.php/ubb/download/Number/377296/filename/KR-WIP.png[img]

wired this way, is the ammeter going to be accurate?

here are the images i've used before, yellow points out the ammeter wiring...hope this helps people out...

EDIT: this is for a '79 model truck

Nacho, thank you for the feedback.

My bulkhead is not great, but it's not as crispy as my ignition harness coming out of the column.The plastic is on the brittle side though, and that worries me. Is there a disadvantage to separating feed to amp gauge OFF of the stock path to the welded splice inside the cab?? Will keeping the feed from alternator to amp gauge on separate path, after the terminal stud in the engine bay, affect correct readings of the amp gauge?

I've even considered cutting out the welded splice in the cab, running the new feed wire from the alternator into a buss under the dash, and then running separate black wires each to the ignition, fuse block, and headlight switch. I could also run the black wire to the amp gauge off this buss. This would be pretty much the same as the stock, welded splice, would it not?

Again, I thank ALL of you for your feedback! As I pull tape off looms, and inspect the unwrapped tape, especially under the dash, I see more wire that has either been cut into by the PO, roughed up by decades of road time, or chew marks by rodents. I will be picking up more spools of correct gauge/color wire soon, with correct connectors, and replacing these. The fuel gauge line and the line from fuse box to bed light switch are 2 good examples of needing replacement. I've aready had to do a hack job of soldering on the orange wire under the dash, where there is a factory welded splice, to repair rodent damage. This, too, will be getting attention, now that the dash is all out.

I need to read up more on building relays into the harness. I'd like to put my heater fan switch on them; at least the High setting.

This is a good learning experience for me. At some point, this truck will be Daily Driver status; soon, I hope. I have a '76 Ramcharger to get into next, and the wiring is bad enough on it that I'm going in with a new wiring harness from someone like Ron Francis or Painless.

I'm travelling right now and can't post as much I'd like due the poor connection. Was trying to post this since couple of hours LOL. Later will get deep into some sugestions.

I'm noticing also you are talking about the shunted system! Need to say the shunted system is different from the full load ammeters. Shunted system or wiring is a remote ammeter reading using miliamperes running throught the 16 gauge wires. You won't get same results wiring a full load system like a shunted systems. Ammeters with shunted systems gets a mounted on coil to amplify the needle movement with just miliamperes thanks to the resistance the shunt provides.

Attached an ammeter to shunted systems, used on Mopars since 75/76 so be careful what diagram you use as a guide!

Ammeter for shunted wiring

The '79 truck diagrams Krautrock posted show it is a typical basic power supply strategy with just a few modifications.
It has internal shunted ammeter - power flows directly through it, not in parallel.
That clears up what Krautrock and probably the OP are dealing with. Thatnks Krautrock!

The power is distributed at the main splice, with two exceptions which we'll come back to later.
When the alternator when its producing power at higher voltage than the battery, it flows through the bulkhead connector to the main splice.
When the battery voltage is higher, power flows from the battery to the main splice by going to the starter relay, through the fusible link, and then through the bulkhead connector, and the ammeter.

This schematic based on a '73 Dart shows the two paths to the main distribution point.


On the '79 truck diagram, that distribution point is the highlighted splice below the headlight switch.
A20A from the bulkhead to the splice is the path current flows from the alternator to where ever it is needed.
A20A from the ammeter to the splice is the final leg of the path current flows from the battery to where ever it is needed, when the alternator can't supply it.
All of the other wires are branches to supply power to different locations. Notice on this truck there are two power supply wires to the ignition switch.

In the previous post, I highlighted wire F38, purple with white stripe. That's one of the two exceptions to distributing power at the main splice.
It comes from the battery positive through a fusible link and the bulkhead connector.
Its power for the 4-way /hazzard flashers. The designers mayt have decided the flashers would generally run when the engine was off, so they conencted them straight to the battery.

The other exception is the DS1 10 gage red wire. I don't know what that is for. Maybe to the horn relay??

One thing that is very different on this truck is the starter relay itself.
I'm not familiar with it. The orange wire seems to be the signal to trip the relay for starting.
The ignition start circuit gets power from the relay, as does of course the starter solenoid.
Just some things we'll have to keep in mind while trouble shooting.

I agree with Rapid Robert on this.
Current climbing with rpms is a a battery with serious problems or some sort of short. Could be in the battery, or the wires crossing or grounding, or inside the starter relay?

Load test the battery and/or put it on a slow charge if its low.


I understand now.
A voltemeter can not be used where an ammeter goes. Ammeters measure current running though them.
Voltmeter has very high internal resistance. It measures potential between two locations. No current flows through it.

Running the alternator output direct to the relay terminal might be useful if running a plow or winch off of the battery - and its a battery that can handle high charge rates.
One danger is no fusible link. If the alternator shorts internally - then the battery will send all the current it can down that new 10 gage wire - until it melts.
Anyway, to answer your other question, the ammeter is no longer accurate when there are two paths from the same point (starter relay) to the distribution point.

If the battery is good, then splice your alternator output to the A20 so the power flow is basically stock, but bypassing the bulkhead connector.
Then visually check over the battery feed/charge wire (S1 etc). While the battery is disconnected, use an ohmeter to see if there's connection to ground (shouldn't be, but that 40 amps indicates something is drawing current that shouldn't be)

I was thinking the bad connection at the bulkhead was making it show 40amps charge. Weird thing is, I was messing with the ammeter (an old aftermarket gauge) and at one point I started it back up and it showed zero charge for a bit...then all the sudden it started showing a high charge rate again...this was while I was troubleshooting connections and right before I realized how burned up the bulkhead connector for the ammeter feed was.

I drove the truck last night with it wired up the way I modified it. Huge difference in all the electrical stuff.
I think the situation slowly got really bad and I didn't notice.

1. Headlights are much brighter now and also, the turn signals blink much faster, even the instrument cluster and signal indicator lights are brighter. The headlights are not flickering at idle while in drive now.
2. The blower motor blows stronger
3. My brake lights and taillights are brighter as well.
4. I thought my wiper motor was going out again, on low they were acting like they were going to stop on the windshield at any moment, now they are working great.

I have an msd on the truck which has it's own power supply wire so the truck has always started fine.





I'm going to have the battery load tested, I just looked and it's almost three years old, a Bosch 65-750BAGM.
I'm also going to do a quick check for shorts, I also think I might wire it up so the ammeter works correctly again but the bulkhead is bypassed and then see if it still shows a high charge rate. That might tell me if the burned up connection was causing that reading.

This truck has aftermarket gauges wired up so replacing the ammeter with a voltmeter would be pretty simple. Like I said, this stuff was all in it when I bought the thing 8 years ago, the gauges are so old some of the plastic inside is dry rotted and sitting in the bottom of the gauge sight window, I think it wouldn't hurt to put a new gauge in there, ammeter or voltmeter.
If I do the voltmeter and leave the alt output going to the relay, I would wire that up so that it has a fusible link inline with the alt feed. The two wires to the ammeter could just both bolt the + side of the voltmeter correct?

I've got to run out now so will write more later.


A high resistance connection on either alternator out or battery charge should reduce the charging.
(The ammeter could have a bad connection - but then it would be getting hot,and current would be reduced)
The terminal studs are pressed, welded or bolted to the shunt plate. If one or both are loose, then there will be a poor connection. Both should be insulated from the housing if it is metal.

One scenario is with high resistance in the circuit, the battery didn't get recharged time and time and again. When a good enough connection was finally made, the battery sucked all the current it could.
https://www.forabodiesonly.com/mopa...ternator-warning.424783/#post-1972341397



Fusible link or links should be placed to protect all wires downstream of the battery. The starter wires are the only exception.

You could tie the two ammeter leads to a voltmeter positive. Disadvantage is the voltmeter is on at all times.

Taking the alternator wires off the starter relay terminal will then let the ammeter only show power flowing to or from the battery.
It also means only one fusible link is needed on the main circuit.

This is what it would look like running except showing with Chrysler ECU.
Don't have time to redraw with MSD, but MSD main feed uses about 1 amps per 1000 rpm.

Nacho, is this more in line with your thoughts. It looks similar to the "parallel" diagram you have posted on the Charger site, except that I left in a 16 gauge FL, and I took out the bulkhead feed, and made a straight shot to the welded splice. But it leaves the original black wire at the amp gauge in place, so that there are now 2 black wires on that post of the amp gauge.

Still unclear if amp gauge would be accurate if both black wires were not on the amp gauge post.

Joe

Its parallel but has a 14 gage Fusible link protecting 12 gage wires.
Need to place a 16 gage Fusible link where the 14 gage link is.
Then the 12 gage wires are better protected. The current 16 gage link can be eliminated.

Yes the ammeter will work as normal. There's only one path to or from the battery - and that's through the ammeter.

A parallel alternator output wire would be like shown below.

A second wire going to the same junction, or equivalent.
In this case its essentially equivalent because the only thing between the two is a wire.
It is a slightly shorte andr more direct route to the battery; so current for charging might prefer it over the route through the bulkhead connector and main splice.

Likewise, a parallel wire from the fusible link to the ammeter battery terminal could be added.

^ i like the mod to just run a parallel wire to the ammeter from the alt output (and likely a parallel wire from ammeter to FL). if my bulkhead weren't so burned up already i think that would be a great simple way to save the bulkhead and keep the ammeter.

on another note, checking for shorts. quick and easy way is to just check for continuity from the circuit to ground with the neg battery terminal unhooked?
ie, I unhooked the neg battery, then, probed from the neg battery terminal to the b+ post on my starter relay, infinite resistance. safe to assume no shorts to ground? still have this wired so that Alt goes to b+ on relay, also from b+ on the relay, a 10g wire into the cab through the firewall, not the bulkhead, and spliced into the power feed/ammeter feed in the wiring harness...

Okay, I understand. The 16 gauge FL on the alternator side was in the alternate 73 Charger/Coronet diagram posted a few pages back. From reading another thread I'd referenced earlier and that diagram, I had assumed that the 16 gauge FL would be necessary on the alternator side, to protect the smaller wiring between it and the amp gauge, if the alternator shorted out, or something else on that side of the amp gauge.

are they available ? maybe similar to the A/B bodies ones ? well I allways try to get the fix as initally was, then make any upgrade. If is brittle for the charging leads, is brittle for the rest too, so If I was you, would try to replace the brittle parts as far is poible.... no matter if with used but better conditions parts ( donors, junkyards )



will get into this later. finally arrived home