68 Barracuda Alternator upgrade.

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CB340

CB340

68 340
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I was hoping someone would help me with this question/ problem. I want to upgrade my 68 Barracuda to a 100 amp alternator but I can't figure out what size shunt I should use, or where to purchase. I want to keep the ammeter functioning, I see a shunt online for 100 amps with a 75mv output, would this work?
I have torn out all the old wiring, under dash and in the engine compartment, everything works fine now (I had major electrical issues). With that said, I'm not interested in cooking the new harnesses, or for that matter the car. The ammeter is bypassed now because I did update to a 75 amp alternator, runs fine, no hot wires, also made connection from alternator to starter relay with 8 gauge, fuseable link attached, cable.
I was hoping to install retro upgrade stereo and amp, as well as a few other electronic toys ( low profile projector headlights)
Can anyone help me out with this question?
1968 Barracuda, 340 engine, updated electronic ignition.
Thanks
 
Fuses have little to do with power output. Size based on the weakest wire or device in the circuit.
Your 100 amp alternator is chicken feed compared to what your car battery. That's the number one item that you want to use a fusible link downstream of.
You may want to redesign the system the system with all those electric loads your planning. Yes, an externally shunted ammeter is good way to monitor flow without routing a main power feed to the instrument area.
What is not clear is what you want the ammeter to show.
Automotive ammeters usually are on the battery circuit - they show whether power is going in or out of the battery, and how much.
It sounds like you're interested in power out of the alternator. If so, then you need a ammeter that reads 0 to 100, one direction only.
 
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i used a gm cs130 with a v-pulley. i had to modify(flatten in a press) the stock triangle bracket and reverse the lower adjusting bracket so it pivots at the lower alternator hole and adjusts at the water pump. Cut spacers as needed and install the gm in line resistor (in place of the charge lamp)on the sensor lead and connector. 2 wires total ,105a and a stock alternator (1989 chevy 2500 5.7)

DSC_0686 (Copy).JPG
 
Ditch the ammeter gage with the 100 amp output alternator. Do the bulkhead bypass, and convert your stock ammeter to volts. I am going to run a 50A mini denso and did just that. Even modded a brand new M&H wiring harness.

Ammeter and alternator output circuit wiring was marginal at best when these old relics were new, even worse now when you ask that much more out of em.
 
Heres stock wiring schematic, and modded one for ammeter bypass. Note how in pic #2 alternator output goes right back to the battery and bypasses the bulkhead connectors, and ammeter is removed from the circuit. This relieves a bunch of electrical stress on the bulkhead connector.

amp-ga18.jpg


Screenshot_20180801-081728.jpg
 
Maybe. If the resistance in both paths is exactly equal. And doesn't do what the OP asked for.
 
In my opinion, May as well convert your OEM amp gauge to a Volts gauge. The rally panel is one of the easier to do. A custom decal for the gauge with volts scale? I can do that too.
 
I did mine, left ammeter scale, adjusted the pot for needle to read slightly above half line at 13.5V i clipped and super glued the stock ammeter needle in place of volt gage needle to keep stock ammeter look. Added a tiny red discharge light to the left of the D on the ammeter face. Used a #50 drill for a tiny hole, jb welded a 12V red led from behind so its not visible until it lights. wired it to my L terminal on the denso.
 
Mattax said:
Fuses have little to do with power output. Size based on the weakest wire or device in the circuit.
Your 100 amp alternator is chicken feed compared to what your car battery. That's the number one item that you want to use a fusible link downstream of.
You may want to redesign the system the system with all those electric loads your planning. Yes, an externally shunted ammeter is good way to monitor flow without routing a main power feed to the instrument area.
What is not clear is what you want the ammeter to show.
Automotive ammeters usually are on the battery circuit - they show whether power is going in or out of the battery, and how much.
It sounds like you're interested in power out of the alternator. If so, then you need a ammeter that reads 0 to 100, one direction only.
Click to expand...
Thanks for the insight!
 
moparmat2000 said:
Ditch the ammeter gage with the 100 amp output alternator. Do the bulkhead bypass, and convert your stock ammeter to volts. I am going to run a 50A mini denso and did just that. Even modded a brand new M&H wiring harness.

Ammeter and alternator output circuit wiring was marginal at best when these old relics were new, even worse now when you ask that much more out of em.
Click to expand...
I did buy a volt meter, will try.
 
Mattax said:
Fuses have little to do with power output. Size based on the weakest wire or device in the circuit.
Your 100 amp alternator is chicken feed compared to what your car battery. That's the number one item that you want to use a fusible link downstream of.
You may want to redesign the system the system with all those electric loads your planning. Yes, an externally shunted ammeter is good way to monitor flow without routing a main power feed to the instrument area.
What is not clear is what you want the ammeter to show.
Automotive ammeters usually are on the battery circuit - they show whether power is going in or out of the battery, and how much.
It sounds like you're interested in power out of the alternator. If so, then you need a ammeter that reads 0 to 100, one direction only.
Click to expand...
I am considering all options, thank you for replying!
 
CB340 said:
I did buy a volt meter, will try.
Click to expand...
OK, if you have Sunpro or similar volt meter in a can, you'll find that screen weighs next to nothing and is captured in the can. So the 2 tiny bits of plastic that the screen attach screws go into are sufficient. Your triangular OEM screen is larger/heavier and more or less floating in this housing, nothing to prevent sagging and/or eventual breaking plastic.
When I would do this conversion as a service for others, I added support gussets to the sunpro gauge frame. First to satisfy myself, repeats to ensure happy customers.
 
The ammeter conversion thread.......... Read all of it, as it covers several cluster styles.

PLEASE don't try and use the original ammeter


Ammeter to Voltmeter...who does it?

If you research some of the 72-ish / newer C barges they went to external shunt meters, which essentially used the harness itself for a shunt. You can download factory service manuals free, from MyMopar

Even "Ma" knew the ammeter wiring was inadequate as back then there was "fleet/ taxi/ police" wiring that was used for optional 65A alternators. The factory bulkhead wires were clipped, and new ones run directly through dedicated grommets in the firewall. This too can be documented in the 69--72ish factory manuals in the wiring section.
 
67Dart273 said:
The ammeter conversion thread.......... Read all of it, as it covers several cluster styles.

PLEASE don't try and use the original ammeter


Ammeter to Voltmeter...who does it?

If you research some of the 72-ish / newer C barges they went to external shunt meters, which essentially used the harness itself for a shunt. You can download factory service manuals free, from MyMopar

Even "Ma" knew the ammeter wiring was inadequate as back then there was "fleet/ taxi/ police" wiring that was used for optional 65A alternators. The factory bulkhead wires were clipped, and new ones run directly through dedicated grommets in the firewall. This too can be documented in the 69--72ish factory manuals in the wiring section.
Click to expand...
Thank you,
I did buy the service manual for this vehicle. I am new at this, exceptionally mechanically inclined, but again new to this much detail. I was hoping that there was a known shunt that would suffice but the more I dig in, the more I know I know nothing! The education I receive for all is greatly appreciated!
It sounds like that there's no quick fix to this question. That's OK, I will learn as I go along.
I was hoping that there was a way to address this common issue by purchasing a manufactured shunt to resolve the problem.
Thanks for your help.
 
Sunpro CP8215 is the volt gage to get for converting your ammeter. I will post pix in a bit. Got some other ideas for taking the devil out of the rallye dash. I also make solid state voltage regulators to eliminate the vibrating points type inside the fuel gage.
 
100amp output i suggest you uprate your alternator output wire to an 8GA wire if you have not done so. Stock alternator output wire on the mopar wiring was i believe 12GA.

If you start running electric fuel pumps, electric fans and really taxing that 100 amper your gonna cook that stock 12ga output wire, and smoke the bulkhead connector. Thats why you uprate the output wire, add fuse link at the battery end, and bypass the bulkhead connector.

You can go to pico wiring products and buy fusable link wire. Typically you want to undwrrate the wire your protecting with a fuse link 2 sizes smaller. So 12GA fuse link wire to protect the 8GA alternator output wire. Typical fusable link length should be about 6 inches long. I crimped ring terminals and soldered mine then used shrink tube over the ends. Made a few to keep as spares in glovebox. Get marine grade multistrand AWG wire. Do not get CCA wire

AWG stands for american wire gage. Its a standard with full copper wire.

CCA is copper clad aluminum. Basically junque wire.
 
Do you want the new alternator to look Stock?
we used to but alternator parts from Ace but they closed their LA warehouse\
My alternator guy Tony is away this weekend but I can ask him next week if you are still in the investigation stage
BTW do eliminate the amp gauge and do the through the firewall mods\there is a reason they call it a firewall also relays for the lights, anything to take loads of the OEM ignition switch and headlight switches, update your wires and fuzes for your new output, extra grounds near loads not relying on the body, etc
 
CB340 said:
Thank you,
I did buy the service manual for this vehicle. I am new at this, exceptionally mechanically inclined, but again new to this much detail. I was hoping that there was a known shunt that would suffice but the more I dig in, the more I know I know nothing! The education I receive for all is greatly appreciated!
It sounds like that there's no quick fix to this question. That's OK, I will learn as I go along.
I was hoping that there was a way to address this common issue by purchasing a manufactured shunt to resolve the problem.
Thanks for your help.
Click to expand...
You would need to find someone who has the equipment to measure the original shunts. Over on moparts there was a guy who offered to do that if you sent him the shunt. Do a search there for external shunt. Nacho was looking into this question.
It still comes back to what you want to measure. If you have over 40 amps going to the battery, there is going to be a problem. An externally shunted ammeter will tell you that, if properly placed. A voltmeter won't. What meters you use all depends on what information you are looking for. Your initial post mentioned many electrical load additions. Some that might run on battery (that is when engine is off). Factory system isn't designed for that. You might want to design a system with an auxilery distribution box and maybe a way to protect the battery from high rates of charging.
 
Wyrmrider said:
Do you want the new alternator to look Stock?
we used to but alternator parts from Ace but they closed their LA warehouse\
My alternator guy Tony is away this weekend but I can ask him next week if you are still in the investigation stage
BTW do eliminate the amp gauge and do the through the firewall mods\there is a reason they call it a firewall also relays for the lights, anything to take loads of the OEM ignition switch and headlight switches, update your wires and fuzes for your new output, extra grounds near loads not relying on the body, etc
Click to expand...
Once you bypass the bulkhead by running the alternator output directly to the battery and put relays for the headlights there's no need to bypass the bulkhead and run the wires in with grommets just make sure the connections are clean and tight and it'll be fine because you don't have the amp draw through it anymore
 
moparmat2000 said:
Once you bypass the bulkhead by running the alternator output directly to the battery and put relays for the headlights there's no need to bypass the bulkhead and run the wires in with grommets just make sure the connections are clean and tight and it'll be fine because you don't have the amp draw through it anymore
Click to expand...
Ignition, heater fan, wipers, parking lights are all still drawing through the bulkhead connector. And any other extras like that stereo amp may or may not be be drawing power through the feeds depending how its wired in. With what the OP asked about, I would not be so confident that the bulkhead connector terminal is fine. Its all depends on the details.
 
All these circuits run through their own individual spades in the bulkhead with the exception of the power feed in, which is now split between 2 wires going in, that do not have the alternator power feeding through as well.

If you do a headlight relay mod that lessens the draw thru the bulkhead further because the brunt of the power feed to the headlights is from the battery right to the relay in the fender and out to the lights. We know the primary point of the relay mod is brighter headlighrs, however The secondary point of the headlight relay is to save the wiring, bulkhead , and switches since with the relays installed it now takes only maybe 1/10th of 1 amp to trip them with the headlight and high beam switch.

Now the factory determined that draw with the factory accessories and Lighting along with a 20A max output alternator to be sufficient for that size bulkhead connector and wire. You have removed the alternator from the equation with a bypass and now have two feeds coming from the battery and going through the bulkhead instead of one so now your amp draw is cut in half through two wires. By this logic if you twisted the two wires together which are 12 gauge you would essentially be pumping the power through a 6-gauge wire at the bulkhead we are keeping them separate because it's easier that way to wire it but you are splitting the amperage between two 12 gauge wires

Now a heavy duty stereo with an amp, you would be running a dedicated amp feed from the battery anyways thru the bulkhead with a rubber grommet.
 
moparmat2000 said:
All these circuits run through their own individual spades in the bulkhead with the exception of the power feed in, which is now split between 2 wires going in, that do not have the alternator power feeding through as well.
Click to expand...
That's an assumption that both wires have exactly the same resistance. Again, which may or may not be so. Otherwise one is loaded more than the other. A wire through a grommet would be the lowest resistance and the best way around those weak terminals. Completely agree that the OP should be considering a system with an auxilery distribution box in the engine compartment and then run power individually to the big draw items being added from there.
 
moparmat2000 said:
Now the factory determined that draw with the factory accessories and Lighting along with a 20A max output alternator to be sufficient for that size bulkhead connector and wire.
Click to expand...
Where are you getting that from?
The factory clearly assumed the an alternator could be providing a lot more than 20 amps to the main distribution point. In fact, for short periods of time it might supply that to the battery alone.

No one is arguing about the lights. The wires from the hi/low are only 18 gage on A-bodies, and only 16 gage before then. That's why the breaker is rated 15 amps. And the number of connections in that circuit is probablematic over time. Relay system is the way to go for these cars if driven night (and not 100% restorations)
 
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