Amp gauge shunt

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bbab3

bbab3

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I have be reading a number of threads related to alternator upgrades. The Mad Electronics method of eliminating the amp guage looks good eliminates the guage, but I really don't want to drill the bulkhead connector and convert my amp guage to a volt guage. My question is, why can't I replicate what came on the Dodge service p/u's? The one I owned had heavy guage wires running through the firewall to the amp guage which had brass shunts bridging the guage terminals to prevent overloading the guage. The alternator in my truck was a giant 100amp style and powered a number of "accessories". Never had any problems, I did remove one of the shunts from the stack for a little bit more movement of the guage needle. There are some aftermarket shunts available to mount remotely and run smaller guage wires to the amp guage, and they come in different amp ratings to adjust needle movement. The alternator I will be using is Denso 120amp off Dodge van. Thanks.
 
Are you running accessories with high current draw? If not why bother.

My 69 has no issues with standard affair. Don’t fix things that are not broke. Use the cash to fix the things you need to.
 
I am running HID headlights, electric cooling fan, and a double din receiver and amp. The alternator should of been a 90 amp. I know what you're saying I have plenty of things to fix!
 
Ok.

Sorry for the fans, mechanical is better IMO. Good luck with it and I will leave it those who have done it.
 
bbab3 said:
I have be reading a number of threads related to alternator upgrades. The Mad Electronics method of eliminating the amp guage looks good eliminates the guage, but I really don't want to drill the bulkhead connector and convert my amp guage to a volt guage. My question is, why can't I replicate what came on the Dodge service p/u's? The one I owned had heavy guage wires running through the firewall to the amp guage which had brass shunts bridging the guage terminals to prevent overloading the guage. The alternator in my truck was a giant 100amp style and powered a number of "accessories". Never had any problems, I did remove one of the shunts from the stack for a little bit more movement of the guage needle. There are some aftermarket shunts available to mount remotely and run smaller guage wires to the amp guage, and they come in different amp ratings to adjust needle movement. The alternator I will be using is Denso 120amp off Dodge van. Thanks.
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"You could." Ma knew that the firewall connector was weak and in cars with optional 65A alternators provided what is known as "police/ taxi / fleet" wiring. This was a modification that DID run the ammeter wires through the firewall separately. Look it up in the service manuals, say, for a 70 Satellite/ Fury etc. Also the big cars somewhere around 70-71 started using external shunt ammeters........GM/ Ford/ Chrysler all did about the same thing.........they used a light movement meter and used the wiring harness itself for the shunt. In the case of Fords, this resulted often in an ammeter that was "numb" that is you could turn on the headlights and not be able to tell if the meter moved at all!!!
 
The final couple of years of A-body ( 75 and 6 I believe ) also had remote shunt amp gauges. I don't have those wiring diagrams.
The problem with doing this to a earlier build is getting the higher amp power supply into the cabin. Unless you route all those wires at the weld splice to the outside of the firewall, You might still have the bulkhead connection melt down.
Drilling the bulkhead connector is only removing the bits of plastic that held those crimped terminals in place so a continuous wire can pass through. This is widely considered necessary regardless which type of gauge is inside.
I suppose you could do like the fleet taxi described above,,, Drill a sperate larger hole through the firewall for another grommet where X number of large gauge high amp wires would pass through.
Edit; After rereading your post, you're considering adding shunts inside, to the back of OEM amp gauge. I suppose that's doable. Some of the above is still for consideration. Good luck with it.
 
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I am considering two different wiring plans. One copying the fleet/service wiring that I had on my Dodge truck. The drawback aside the addition of the heavier gauge wiring is how many brass shunts to add to the back of the amp guage due to access, obviously more is safer. The other option is a remote shunt (they come in different amp ratings) mounted in the engine compartment running two 14ga wires to the amp guage and one 6ga from the shunt to a insulated terminal post mounted on the passenger side of the bulkhead to replace the splice connection. The problem is the amp rating of the shunt needed to not fry the guage.
 
Mad Electronics sells an insulated terminal post that's fairly well protected that I plan on using to prevent from having to many connections stacked on the starte relay terminal. While on the phone I am going to run this idea by them to at least see if it's feasable.
 
I don’t understand why you would use shunts on the stock ampmeter if that is what you are proposing. The stock ampmeter only works correctly with the full load current going through it.

Shunts must be matched to a meter that is designed for the shunt. An ampmeter that uses a remote shunt measures the voltage drop across the shunt (it is really a voltmeter). The stock gauge has the shunt built in already, so it measures the whole current in the wire.
 
Mike69cuda said:
I don’t understand why you would use shunts on the stock ampmeter if that is what you are proposing. The stock ampmeter only works correctly with the full load current going through it.

Shunts must be matched to a meter that is designed for the shunt. An ampmeter that uses a remote shunt measures the voltage drop across the shunt (it is really a voltmeter). The stock gauge has the shunt built in already, so it measures the whole current in the wire.
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There's no reason you could not add more shut. It would simply increase the capacity of the meter while making it less sensitive. HOWEVER you'd BETTER solder/ silver solder the studs and make darn sure the connections are better than factory

If you "must" ammeter (and I would prefer them over voltmeters) a completely remote shunt is much better.........keep the heavy current out of the bulkhead and avoid voltage drop
 
bbab3 said:
I am considering two different wiring plans. One copying the fleet/service wiring that I had on my Dodge truck. The drawback aside the addition of the heavier gauge wiring is how many brass shunts to add to the back of the amp guage due to access, obviously more is safer. The other option is a remote shunt (they come in different amp ratings) mounted in the engine compartment running two 14ga wires to the amp guage and one 6ga from the shunt to a insulated terminal post mounted on the passenger side of the bulkhead to replace the splice connection. The problem is the amp rating of the shunt needed to not fry the guage.
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What you need to experiment with this is some type of "big" resistor and test meter such as a starter/ battery "carbon pile" tester or a dual meter starter/ battery/ alternator tester. You can find them on C/L often fairly cheap. I have I forget, sun or snap-on, had bad push button (latching) switches. I simply hard wired it to read voltage and current and "there it is" LOL
 
Ok, I guess that is technically correct, but would it be functional? How would you know what the ampmeter scale was? As I am writing this, I am thinking that there is no scale on the ampmeter anyway, so maybe I don’t really have a point....
 
To be honest I am not a automotive electrical engineer, just knowable enough to be dangerous. What Dodge in the late '70's to '80's with pickups with the 100amp alternators was to use the same amp gauge as they used with the 60amp alternators. The shunts were brass sheet metal pieces that bridged the amp guage terminals to compensate for the higher amps due to the larger guage wiring that bypassed the bulkhead connections, and the increased amp output. I am using a Denso alternator and brackets from '90's Dodge van that is rated at 120amps. That's why I am looking at the use of shunts. Granted, I could modify tha amp guage in my rallyy dash cluster. But since the factory made it work on pickups for a number of years or fleet/service trucks I thought about finding out why it's not the preferred method when upgrading to a bigger alternator to run newer accessories. What I don't know is what size shunt, and if I am just barking up the wrong tree!
 
What is the fascination with the ammeter? Just bypass the POS, run all the stock wire as OEM and install a protected charge wire from alternator to starter relay or sub-bus point.

Get a voltmeter that plugs into a cig lighter to monitor charging system.
 
crackedback said:
What is the fascination with the ammeter? Just bypass the POS, run all the stock wire as OEM and install a protected charge wire from alternator to starter relay or sub-bus point.
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That is what I was trying to get to. The ampmeter seems to have plenty of range for most, what is the point in putting more shunts on it? Probably would be hard to get it to work properly. A remote shunt under the hood may be a nice idea, but that would involve modifying the stock ampmeter. Seems like a lot of trouble for a uncertain gain.
 
The reason for the thread was to find out if anyone copied the factories solution of a increased amp alternator installation in an a-body. My main concern with any wiring modification is fire, already watched one car burn to the ground due to a failed Pertronics ignition module. I'm not married to my 50 year old amp guage, just looks like a simple fix. Probably going to run hot 6ga wire from a insulated terminal block wired directly to starter relay/alternator to another insulated terminal block under the dash. Then eliminate the under dash splice and gut my amp guage and do the Sunpro volt guage modification on the ralley gauge. Just want do it right the first time.
 
Mike69cuda, on my Power Wagon the amp guage hardly moved, even when the HID off-road lights were switched on/off. I removed one brass shunt at a time to increase the neddle movement. Still the same concern fire. Resistance=heat=fire.

Crackedback, a volt guage in the cigarette light would work. My dash frame had so many holes I got carried away welding them up and eliminated the ashtray looks a lot cleaner!
 
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Mike69cuda said:
Ok, I guess that is technically correct, but would it be functional? How would you know what the ampmeter scale was? As I am writing this, I am thinking that there is no scale on the ampmeter anyway, so maybe I don’t really have a point....
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LOL. I've heard that A body ammeters were supposed to be somewhere around 40-45A full scale, but I bet that was never officially printed anywhere
 
I parted out a couple c body’s once, I think 65 and 66 fury’s. Both had heavy duty threaded bulkhead connections for the wires to and from the amp gauge- separate from the main bulkhead connector. I always wondered why they didn’t do that on all vehicles instead of that shitty setup they used on most everything.
 
jas0162 said:
I parted out a couple c body’s once, I think 65 and 66 fury’s. Both had heavy duty threaded bulkhead connections for the wires to and from the amp gauge- separate from the main bulkhead connector. I always wondered why they didn’t do that on all vehicles instead of that shitty setup they used on most everything.
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Actually they did that on A bodies for one or two years I can never remember............63--4--5--6 seems like they did one, skipped a year, went back and then abandoned the idea.
 
image.jpeg
Since I have the flu and have a need to keep myself busy I thought I would elaborate with some crude drawings to better explanation my ideas. The first one "plan a" shows the brass shunts like was used on my Power Wagon plus two insulated terminals to clean things up and eliminate the welded splice.
image.jpeg

"Plan b" above shows the use of an external shunt like Stewart Warners uses with their amp gauges that are rated to 100 and 300amps.

Also here's the link that made me consider keeping the amp guage in my ralley dash.
Bullet-Proof Your Ammeter (A 'How To') - DodgeTalk : Dodge Car Forums, Dodge Truck Forums and Ram Forums
This shows how to improve the conductivity of the guage.

Hope this helps.
 
One more thing one of the threads I read Trailbeast posted about using a 30amp DC breaker versus a fuse-able link. Which makes sense, they won't burn just pop. For a 120 amp alternator what's the appropriate size for a charging circuit running 8ga wire?
 
bbab3 said:
I am running HID headlights, electric cooling fan, and a double din receiver and amp. The alternator should of been a 90 amp. I know what you're saying I have plenty of things to fix!
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I was going to post some references to externally shunted ammeters, '76 A-bodies had them and you can buy new from places like Aircraft Spruce or Jamestown Supply.
But I think that the main issue you should be focused on is how to get power to all that equipment without overloading any wires or connections. The ammeter is not the whole issue. Its that wire is being asked to handle too many loads.
The stock system had two feeds; Battery and Alternator. The battery feed became the charging feed when the engine was running.
There's just one fusible link needed, and if everything is working right, the only loads it sees are short term.
That Ammeter, fusible link, and connections should only be used for starting and charging.
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When electric fans and other equipment is added to the charge wire, its going to carry more than just the recharge current and the ammeter isn't going to reflect the charge/discharge situation.
upload_2019-1-1_18-5-17.png


Having one alternator feed to the inside distribution point, and another to the new distribution box in the engine compartment shortens the path, reduces the connections, and splits the load. If you want an ammeter to show the battery draw and charge rates, an external shunt could be used (like the '76 A-bodies had). Something like this.
upload_2019-1-1_18-23-54.png
 
bbab3 said:
"Plan b" above shows the use of an external shunt like Stewart Warners uses with their amp gauges that are rated to 100 and 300amps.
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heh. we were writing at the same time.
IMO, you don't want the battery charging at anything more than 30 amps, and even that for less than a minute. 5 amps or less. So I guess what I'm saying is the ammeter range needed depends on how the battery(s) will be used and charged. If it, or they will be getting deep cycled and put through heavy load, probably need a regulated charge and maybe one of the leece neville alternators.

With all the power distribution inside, as you drew, an internally shunted ammeter could work. The question is whether the ammeter and everything else in that line would stay cool enough when running on battery alone, and then again when recharging. It still might be good to have a dedicated charging wire on the engine compartment side - and use a external shunt for the ammeter.
 
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