A 4 pin ballast resistor thats correct.

[bills73duster]

Does anyone have a clue where I can purchase a correct ballast resistor with the correct upper (5.0 ohm) and correct lower (1.2 ohm) pin readings?
I've returned 2 recently with ohm readings, 8.1 and 5.0 respectively.

 

[toolmanmike]

First of all, start a Parts Wanted ad in the Marketplace forums. Second, contact Halifaxhops through a DM.

 

[halifaxhops]

I have plenty of them Mopar and NORS. PM me Just FYI the real ones have the ohms rating on one side of the flag terminals. Have to take a picture.

 

[bills73duster]

I read last night that "standard motor" products garrenteed a ohm reading of
1.15 to 1.38 on the lower and 4.75 to 5.75 on the upper. Still aftermarket but closer to correct .
I'm considering it.
.

 

[Dana67Dart]

Just asking... Do you still have a true 5 pin ECU?

if not the 4 pin ballast is not necessary. You could get a 4 pin for looks but only be concerned with the coil side resistance being correct.

Also if you have other than a stock coil the coil side resistance might also be a different requirement then OEM

 

[Vaanth]

Does anyone have a clue where I can purchase a correct ballast resistor with the correct upper (5.0 ohm) and correct lower (1.2 ohm) pin readings?
I've returned 2 recently with ohm readings, 8.1 and 5.0 respectively.

I read last night that "standard motor" products garrenteed a ohm reading of
1.15 to 1.38 on the lower and 4.75 to 5.75 on the upper. Still aftermarket but closer to correct .
I'm considering it.
.

To ensure the resistance of a ballast resistor is correct, or as desired, measuring using proper technique is required, particularly with modern, current or recently produced parts. The listed 1.13 - 1.38 ohm and 4.75 - 5.25 ohms resistance ranges quoted from Standard Motor Products for their replacement resistor, part number RU-12, or RU-12T, is essentially the tolerance range specified by Chrysler. If it was them quoting it 40 years ago, I would grant it more merit than today. However, the measured numbers of 8.1 and 5.0 ohms (auxiliary and primary/compensating), occurring twice, seems off even for current parts, so perhaps it points to possible measurement technique. Verify the test equipment, and depending on the meter used, account for test lead and connection resistance. If the technique is sound, it appears modern parts might be getting even worse.

Older production NOS parts can typically be better at meeting original specifications and performance expectations than current parts, even from the same manufacturer. Checking NOS parts sources, scouring eBay, etc. one can find older good parts, but as mentioned, Halifaxhops (Ray) can provide tested and verified NOS parts which would more readily meet the original and desired specification. Also, as Ray noted, the resistance of each resistor might be stamped on one of the terminals, perhaps more in the past than now. This can be an initial identifier, but proper measurement verification should be done. Modern parts can require more scrutiny. I don’t use modern parts myself, unless I really have to do so. If new is the only alternative, perhaps try NAPA/Echlin. Echlin was historically, usually better than Standard, and is still made. However, Standard now owns Echlin, or much of it. The parts might be built to a higher level though, especially if NAPA is specifying for it.

Some additional information follows.

---

Chrysler Electronic Ignition Four Terminal Ballast Resistors

Chrysler used two different four terminal "dual" ballast resistors with the "5-pin" electronic control units (ECUs) in 1971 - 1979. The two different ballast resistors are listed in the following table:

3656199, CH455	1971 - mid 1975	4 terminal	0.5/5 ohms	Open back primary resistor. Sealed back auxiliary resistor.
3874767, CH456	Late 1975 - 1979	4 terminal	1.25/5 ohms	Sealed back for both resistors.

The primary resistance was increased with the later resistor, which also had less thermal change with the primary resistor compared to the earlier version. The two resistors were treated separately for their applications initially, but, although higher in primary resistance, the later resistor, number 3874767, became the service replacement for the previous resistor number 3656199. With all else the same, the higher primary ballast resistance lessens total delivered spark energy some, but Chrysler determined this to be acceptable for the production application.

The tolerance rating of the resistors, at 70-80 degrees Fahrenheit, by Chrysler is as follows:

3656199:

• 0.55 ohm nominal, but usually listed as 0.5 ohm, tolerance range: 0.50 - 0.60 ohm
• 5.00 ohms nominal, tolerance range: 4.75 - 5.25 ohms

3874767:

• 1.25 ohm nominal, sometimes listed as 1.2 or 1.5 ohm, tolerance range: 1.12 - 1.38 ohm
• 5.00 ohms nominal, tolerance range: 4.75 - 5.25 ohms

The early aftermarket manufacturers made replacements for the 3656199 resistor in the 0.5/5 ohms rating. With the new 3874767 resistor, initially, the same manufacturers made their replacement in the 1.25/5 ohms rating. Over time, the 3874767 rating supplanted the 3656199 rating, at times with different part numbers,but largely re-using the same part number.

The following table shows aftermarket replacement resistor part numbers. The numbers are repeated for both resistors for several manufacturers as the application specification was combined:

3656199	Wells CR-105/CR1105 Standard RU-12/RU-12T E-tron RU-12 Echlin ICR 24 Big A 30-351 WVE 6R1008 Airtex 6R1008 Delco Remy C1102/1972459 Filko CH400 Borg Warner RUE-1 Niehoff AL125BCM, AL125B Kem FR57 Accel 150351 Kmart CR1105 Holley 35-19 Sorensen CE-3 P&D RU-13 GP EL-401	4 terminal	0.5/5 ohms
3874767	Standard RU-12/RU-12T Niehoff AL125BCM, AL125B Kem FR57 E-tron RU-12 Echlin ICR 24 WVE 6R1008 Airtex 6R1008 GP EL-401 Accel 150351 Filko CH400 Auto-Tune E-221 E-tron RU-12 Sorensen CE-3	4 terminal	1.25/5 ohms

---

Measuring Low Resistance

When measuring low resistances, including ballast resistors, account for the resistance of the test leads connected to the measuring device. This can be done by shorting the leads together, noting the resistance, and subtracting it from the measurement readings, or use the meter's relative setting (if equipped) similarly with the lead shorting, or use a meter that measures conductance and convert accordingly, or use a four wire ohms measurement setup with the appropriate device. An analog meter can also be used but resolution might be lacking on the lower resistance, The same tst lead considerations hold true.Also because the analog meter has to drive the needle, a weak battery can hamper the measurement.

The following images show a Fluke 27 and a Fluke 8520 being used to measure a Chrysler 3874767 which has never been used. Temperature = 72 degrees Fahrenheit.

Resistor to be measured:

Checking test lead resistance. In this case, my lead resistance is lower than the resolution of the meter (< 0.1 ohm). Any number measured here is to be subtracted from subsequent measurements, or the meter zeroed to remove it.

Measuring the 1.2 ohm primary, or compensating, resistance:

Measuring the 5.0 auxiliary resistance:

Double checking my meter at 1.00 ohm as verification, using my General Radio 1433M Decade Resistance:

The next set of images show a 4-wire ohms measurement using the 8520 meter. This is overkill for a ballast resistor, and might not be available, but it shows the fuller readings for demonstration purposes. With the 4-wire measurement technique, the test lead resistance is not (usually) a factor. The meter uses a constant current source with voltage measured at the measuring point to calculate resistance, which removes the test lead resistance from the measurement itself. A two-wire meter also does this but inside, behind the test leads, hence their effect on the measurement.

Connection at the resistor being measured:

Measuring the 1.2 ohm primary, or compensating, resistance:

Measuring the 5.0 auxiliary resistance:

Double checking my meter at 1.00 ohm as verification, using my General Radio 1433M Decade Resistance:

General Radio 1433M Decade Resistance used to verify meters:

---

For more information about Chrysler’s electronic ignition, including ballast resistors, and their use with other components, refer to Chrysler Electronic Ignition.

 

[RustyRatRod]

To ensure the resistance of a ballast resistor is correct, or as desired, measuring using proper technique is required, particularly with modern, current or recently produced parts. The listed 1.13 - 1.38 ohm and 4.75 - 5.25 ohms resistance ranges quoted from Standard Motor Products for their replacement resistor, part number RU-12, or RU-12T, is essentially the tolerance range specified by Chrysler. If it was them quoting it 40 years ago, I would grant it more merit than today. However, the measured numbers of 8.1 and 5.0 ohms (auxiliary and primary/compensating), occurring twice, seems off even for current parts, so perhaps it points to possible measurement technique. Verify the test equipment, and depending on the meter used, account for test lead and connection resistance. If the technique is sound, it appears modern parts might be getting even worse.

Older production NOS parts can typically be better at meeting original specifications and performance expectations than current parts, even from the same manufacturer. Checking NOS parts sources, scouring eBay, etc. one can find older good parts, but as mentioned, Halifaxhops (Ray) can provide tested and verified NOS parts which would more readily meet the original and desired specification. Also, as Ray noted, the resistance of each resistor might be stamped on one of the terminals, perhaps more in the past than now. This can be an initial identifier, but proper measurement verification should be done. Modern parts can require more scrutiny. I don’t use modern parts myself, unless I really have to do so. If new is the only alternative, perhaps try NAPA/Echlin. Echlin was historically, usually better than Standard,and is still made. However, Standard now owns Echlin,or much of it. The parts might be built to a higher level though, especially if NAPA is specifying for it.

Some additional information follows.

---

Chrysler Electronic Ignition Four Terminal Ballast Resistors

Chrysler used two different four terminal "dual" ballast resistors with the "5-pin" electronic control units (ECUs) in 1971 - 1979. The two different ballast resistors are listed in the following table:

3656199, CH455	1971 - mid 1975	4 terminal	0.5/5 ohms	Open back primary resistor. Sealed back auxiliary resistor.
3874767, CH456	Late 1975 - 1979	4 terminal	1.25/5 ohms	Sealed back for both resistors.

The primary resistance was increased with the later resistor, which also had less thermal change with the primary resistor compared to the earlier version. The two resistors were treated separately for their applications initially, but, although higher in primary resistance, the later resistor, number 3874767, became the service replacement for the previous resistor number 3656199. With all else the same, the higher primary ballast resistance lessens total delivered spark energy some, but Chrysler determined this to be acceptable for the production application.

The tolerance rating of the resistors, at 70-80 degrees Fahrenheit, by Chrysler is as follows:

3656199:

• 0.55 ohm nominal, but usually listed as 0.5 ohm, tolerance range: 0.50 - 0.60 ohm
• 5.00 ohms nominal, tolerance range: 4.75 - 5.25 ohms

3874767:

• 1.25 ohm nominal, sometimes listed as 1.2 or 1.5 ohm, tolerance range: 1.12 - 1.38 ohm
• 5.00 ohms nominal, tolerance range: 4.75 - 5.25 ohms

The early aftermarket manufacturers made replacements for the 3656199 resistor in the 0.5/5 ohms rating. With the new 3874767 resistor, initially, the same manufacturers made their replacement in the 1.25/5 ohms rating. Over time, the 3874767 rating supplanted the 3656199 rating, at times with different part numbers,but largely re-using the same part number.

The following table shows aftermarket replacement resistor part numbers. The numbers are repeated for both resistors for several manufacturers as the application specification was combined:

3656199	Wells CR-105/CR1105 Standard RU-12/RU-12T E-tron RU-12 Echlin ICR 24 Big A 30-351 WVE 6R1008 Airtex 6R1008 Delco Remy C1102/1972459 Filko CH400 Borg Warner RUE-1 Niehoff AL125BCM, AL125B Kem FR57 Accel 150351 Kmart CR1105 Holley 35-19 Sorensen CE-3 P&D RU-13 GP EL-401	4 terminal	0.5/5 ohms
3874767	Standard RU-12/RU-12T Niehoff AL125BCM, AL125B Kem FR57 E-tron RU-12 Echlin ICR 24 WVE 6R1008 Airtex 6R1008 GP EL-401 Accel 150351 Filko CH400 Auto-Tune E-221 E-tron RU-12 Sorensen CE-3	4 terminal	1.25/5 ohms

---

Measuring Low Resistance

When measuring low resistances, including ballast resistors, account for the resistance of the test leads connected to the measuring device. This can be done by shorting the leads together, noting the resistance, and subtracting it from the measurement readings, or use the meter's relative setting (if equipped) similarly with the lead shorting, or use a meter that measures conductance and convert accordingly, or use a four wire ohms measurement setup with the appropriate device. An analog meter can also be used but resolution might be lacking on the lower resistance, The same tst lead considerations hold true.Also because the analog meter has to drive the needle, a weak battery can hamper the measurement.

The following images show a Fluke 27 and a Fluke 8520 being used to measure a Chrysler 3874767 which has never been used. Temperature = at 72 degrees Fahrenheit.

Resistor to be measured:
View attachment 1716501661


Checking test lead resistance. In this case, my lead resistance is lower than the resolution of the meter (< 0.1 ohm). Any number measured here is to be subtracted from subsequent measurements, or the meter zeroed to remove it.
View attachment 1716501667


Measuring the 1.2 ohm primary, or compensating, resistance:
View attachment 1716501659

Measuring the 5.0 auxiliary resistance:
View attachment 1716501679

Double checking my meter at 1.00 ohm as verification, using my General Radio 1433M Decade Resistance:
View attachment 1716501664

The next set of images show a 4-wire ohms measurement using the 8520 meter. This is overkill for a ballast resistor, and might not be available, but it shows the fuller readings for demonstration purposes. With the 4-wire measurement technique, the test lead resistance is not (usually) a factor. The meter uses a constant current source with voltage measured at the measuring point to calculate resistance, which removes the test lead resistance from the measurement itself. A two-wire meter also does this but inside, behind the test leads, hence their effect on the measurement.

Connection at the resistor being measured:
View attachment 1716501665

Measuring the 1.2 ohm primary, or compensating, resistance:View attachment 1716501660

Measuring the 5.0 auxiliary resistance:
View attachment 1716501666

Double checking my meter at 1.00 ohm as verification, using my General Radio 1433M Decade Resistance:View attachment 1716501663

General Radio 1433M Decade Resistance used to verify meters:
View attachment 1716501662

---

For more information about Chrysler’s electronic ignition, including ballast resistors, and their use with other components, refer to Chrysler Electronic Ignition.

You really should come to a club meeting sometime. You don't get out enough. lol

 

[halifaxhops]

Darn Vaanath hell of a reference library you put together!

 

[bee1971]

And to further complicate

That same Mopar Part # with a .5 OHM Primary Side

 

[RustyRatRod]

Darn Vaanath hell of a reference library you put together!

I told him in the other thread he needs to get out more. lol

 

[toolmanmike]

How much does the resistance change between testing in July and January? Asking for a friend.

 

[Dana67Dart]

How much does the resistance change between testing in July and January

How much does it change with 2 amp load..... Enough to drop 12v down to 5-6. But it gets really hot in the process.