Ammeter question

[Rubatoguy]

I understand that at some point the wiring of the ammeter gauge was made with an external shunt. Somewhere around '73-'75 on.
Does anyone know where to find (or have) one of these? Or a part number?

thank you,
Todd

 

[Vaanth]

I understand that at some point the wiring of the ammeter gauge was made with an external shunt. Somewhere around '73-'75 on.
Does anyone know where to find (or have) one of these? Or a part number?

thank you,
Todd

The 1971 C-bodies and Imperial were the first equipped with the shunt ammeter system. B-bodies switched to the shunt ammeter system in 1975. A-bodies switched to the shunt ammeter system in 1976. The E-bodies never switched. All F/M/J-bodies and R-bodies were shunt ammeter systems. Dodge trucks switched in 1981.

Ammeter part numbers vary depending on the model and instrument cluster. The 1971 Chrysler models' ammeter part number is 2985674.

Announcement in the 1971 Chrysler Service Highlights:

 

[Rubatoguy]

That is great information, thank you! Are the service highlights available anywhere? The ammeter in my car is currently bypassed and at some point the alternator was replaced with a high output 70 amp alternator, so I don't think it would be a good idea to hook up the stock ammeter with a 70 amp alternator. Is that correct?

 

[72RoadRunnerGTX]

I understand that at some point the wiring of the ammeter gauge was made with an external shunt. Somewhere around '73-'75 on.
Does anyone know where to find (or have) one of these? Or a part number?

thank you,
Todd

The “external shunt”? A section charge path wiring between two splices in the engine harness acts as the external shunt for the later externally shunted ammeters. It was not a serviceable part, having its own part number.

 

[CBODY67]

MasterTech Service Highlights can be found at www.mymopar.com (might have to input that address manually.

Enjoy!
CBODY67

 

[Vaanth]

That is great information, thank you! Are the service highlights available anywhere? The ammeter in my car is currently bypassed and at some point the alternator was replaced with a high output 70 amp alternator, so I don't think it would be a good idea to hook up the stock ammeter with a 70 amp alternator. Is that correct?

The ammeter itself contains the shunt, which is a wound coil of relatively fine wire. The feed wiring which is tapped off the cable from the alternator is typically 20 AWG wire. As shown in the service highlight, with a 40 amp example, the current divides between the large alternator cable and the small wiring through the shunt. The current through the shunt is quite small compared to the alternator cable. 1971 Chrysler models were originally equipped with 60 amp alternators. A step up to 70 amps is not much. If the current demand did ever exceed 60 amps, the ammeter might respond with the needle over the maximum marking, but possibly not considering connection resistance. The amount of current divided from that level of charge current still would not exceed the rating of the 20 AWG wires, especially considering connection resistance. Resistance causes heating, but the full current through the shunt circuit is less than 1.5 amps at 60 amps full charge or discharge. Technically, the ammeter and circuit rating, in ideal condition, would be exceeded.... practically, not. I would not have an issue with using the shunt ammeter with a 70 amp alternator, but others must make their own determination based on all the details.

There are a few Service Highlights at The 1970 Hamtramck Registry Library Page (1970 - 1974). I have original print copies from the early 1960s through the 1980s with a few gaps.

 

[72RoadRunnerGTX]

That is great information, thank you! Are the service highlights available anywhere? The ammeter in my car is currently bypassed and at some point the alternator was replaced with a high output 70 amp alternator, so I don't think it would be a good idea to hook up the stock ammeter with a 70 amp alternator. Is that correct?

The current flowing though the charge/distribution wiring/components is determined by the loads, not the alternator capacity. On a healthy correctly loaded system, fully charged battery, there should be little to no current flowing through the ammeter while in operation no matter the alternator capacity. Unless the loads exceed the alternator capacity.

The ammeter itself contains the shunt,...

By definition, with an externally shunted ammeter, the shunt is “external” to the ammeter.

 

[CBODY67]

Yes, a common mis-perception is that all of the alternator capacity is happening all of the time, when it is only as great as the needs placed on it. Just like an ignition coil.

 

[Big_John]

Yes, a common mis-perception is that all of the alternator capacity is happening all of the time, when it is only as great as the needs placed on it.

^This^

It's probably one of the most common misunderstandings that I see here.

That, and the thought you need some alternator that puts out enough to light a small city.