Old ignition module - how to clean up, and will they still work (well) ?

[Big_John]

based on your write-up I'm not sure if the 1.8 ohm coils (that were the standard coil for points) was also the same coils for the early ECU setup.

I've seen an 8-page tech writeup by Chrysler where they explain the ECU and show the 3 ballast resistors used. Two of them were dual-resistor. Of those, the coil resistor was different. One was an exposed wire-wound with a value of 0.5 ohms. The other was potted with a value of 1.25 ohms. I'm curious why there were 2 types. The points setup used the single 0.5 ohm resistor I think. Either they went with the 1.25 ohm resistor to pair it with a different coil (with a resistance less than 1.8 ohms) or they wanted to limit the current through the 1.8 ohm coil (maybe for the benefit of the ECU).

The big difference is in the older style, like you have, has 5 pins and requires the dual resistor. The newer 4 pin doesn't need it.

One thing I learned was the 4 pin is a "plug and play" that so there's no wiring change in a dual resistor car, but when I found my '70 had the 4 pin and the dual resistor, I made the change to the wiring to the single resistor.

From what I've read, some of the aftermarket ECU boxes have a fake 5th pin to stop returns from people not understanding this.

This is the best explanation I've ever read on how the dual resistor system works versus the single, complete with diagrams. I still had to read it a few times to wrap my brain around it as I had a different understanding of how it worked.

BTW, the comment of "electron flow" is that electrons flow from negative to positive. Since I think you (@MoPar~Man ) work in the electronics field, you probably understand that, but others may not.

The following is a quoted explanation and not from me.

"When you START the car with a 4 terminal ballast, "things are a trick." There is no "ignition run" power during start, the coil PLUS is powered through the ballast bypass (brown, IGN2) circuit. So the power BACKFEEDS through the resistor to power the ECU during crank. VERY POOR DESIGN in my opinion

Here is the circuit. The "ignition run" at lower right is DEAD during cranking. Only power to the circuit comes from "Ignition 2" pink in the diagram

Current flow from coil is from ECU ground, through box switching transistor, to coil NEG and through coil, out coil + and back to battery through the pink "ign 2"

Box circuit is from ECU ground, out pin 1, through resistor from right to left lower section, out resistor and back to battery on pink

Other section is s from ECU ground, out pin 3 (blue) to top section of resistor, through top section from left to right, through bottom section from right to left, and back to battery on pink.

This is "properly described" as neg to pos electron flow"

"The vast majority of ECU boxes you run into are ACTUALLY more modern 4 pin boxes, which only require a TWO pin resistor, but "can" run with a 4 pin installed. The "other half" is simply not used

This simplified circuit omits the "ign2" bypass and shows the "run" as "existing wire" off to top right. THIS CIRCUIT shows that the coil resistor is same as points.........feeds from points (transistor switch) up through coil, up through resistor, and back to the battery. "Just like" the 4 pin, in start, the resistor has to feed the box to power it during cranking. The "existing" wire is dead. ONLY POWER is IGN2 "bypass" being fed to coil+ during "start.

Here is how the 2 pin resistor start circuit works:

From ground, through the ECU box, through the switch, through the coil, out coil + to the bypass "start" wire

From ground through the ECU, out pin "blue" up through the resistor, and back to battery on "start" wire. This is a misnomer, it is IGN2, not the "start" wire"

 

[MoPar~Man]

Yes, but I was noting that for the dual-resistor ballast, there seems to have been 2 varients of those. The higher-value resistor (5 ohms) was the same, but the lower-value resistor (the one used by the coil) was different. For one varient, it was 0.5 ohms, for the second it was 1.25 ohms. I know that later the the second resistor (5 ohms) went away, along with one of the pins on the ECU. I'm just wondering why the change in the coil resistor.

 

[Vaanth]

@Vaanth based on your write-up I'm not sure if the 1.8 ohm coils (that were the standard coil for points) was also the same coils for the early ECU setup.

I've seen an 8-page tech writeup by Chrysler where they explain the ECU and show the 3 ballast resistors used. Two of them were dual-resistor. Of those, the coil resistor was different. One was an exposed wire-wound with a value of 0.5 ohms. The other was potted with a value of 1.25 ohms. I'm curious why there were 2 types. The points setup used the single 0.5 ohm resistor I think. Either they went with the 1.25 ohm resistor to pair it with a different coil (with a resistance less than 1.8 ohms) or they wanted to limit the current through the 1.8 ohm coil (maybe for the benefit of the ECU).

The Chrysler ignition ballast resistor used in the 1960s through 1972 for point systems, part numbers 2095501, 2196316, or 2275590, is an open back, ceramic power resistor. This ballast resistor measures 0.5 ohms and has specific, expected thermal design properties for controlling current to the coil and through the points.

Ballast resistor use carried over into Chrysler's electronic ignition. Chrysler’s point ignition replacement electronic ignition, which first appeared in late 1971 340 with manual transmission models (Ref. Technical Service Bulletin D71-8-9), introduced the four-terminal, dual ballast resistor, part number 3656199.

The primary, or compensating, side of the dual resistor used with the electronic control module (ECU) is the same type as the earlier point systems with an open back, ceramic housed, wire wound nominal 0.55 ohm resistor. The resistor still performed the same thermal adjusted coil current/voltage stabilization. The resistor also limits the current through the power transistor of the ECU, protecting it, similar to the same action with points.

The other side of the ceramic case dual ballast resistor houses an enclosed "non-thermal" auxiliary resistor which measures 4.75 - 5.75 ohms at 70-80 degrees Fahrenheit. This nominal, five ohm resistor is connected to the "fifth pin" of the ECU. Internal to the ECU, the auxiliary resistor connects to the collector lead of the driver transistor for the main power transistor and part of its biasing. It limits overall current from the 12 volt supply. The other four pins of the ECU connect to the dual lead of the distributor pickup coil, the 12 volt Ignition Run primary power, and the lead to the negative side of the coil for the coil switching action, similar to the connecting lead from the distributor points in the old system.

The same coil with the same primary resistance and part number, 2495531, as used with the 1964 through 1972 contact points systems carried over to be used in production with the Chrysler electronic ignition system. The 2495531 coil primary resistance is the same 1.6 - 1.79 Ω for the 2444242 type coil and 1.34 - 1.55 Ω for the 2444241 type coil. Both were supplied to Chrysler and used through 1979.

The same type of coil, part number 2495531, et.al. as used with the points system, continued in production with the ECU. The combined total resistance of the coil, ballast resistor, and the marginal wiring, connections, and effective transistor resistance still add to about two ohms. The ~two-three ohm total, which varies as the ballast resistor varies, limits the transistor and coil primary current to about four-six amps peak, although the transistor can actually sink more current.

In 1972, electronic ignition was extended to the following applications:

• Standard on 1972 A-bodies, B-bodies, and E-bodies with high performance engines.
• Standard on 1972 Imperials
• Standard on 1972 California C-bodies with 360 two barrel, 400 two barrel, and 440 four barrel engines.
• Optional on 1972 non-California C-bodies with 360 two barrel, 400 two barrel, and 440 four barrel engines.
• Optional on 1972 Dodge light trucks and compact vans, starting in January 1972.
• Standard on 1972 motor home 318-3 and 413-1 engines starting in June 1972.

Different versions and part numbers of the ECU were used in 1972 from 1971, including some with an engine speed limiter which was denoted by heat sink color. The non-limited 3438850 has a gold heat sink. The red heat sink unit, part number 3656127 limits RPM to 5000-5200 and was used on 400 and 440 high performance manual transmission applications. The blue heat sink unit, part number 3656128 limits RPM to 5300-5500 and was used on 340 manual transmission applications.

In 1973, electronic ignition became standard on all domestic Chrysler vehicles. The speed limited ECUs were dropped from production. ECU part number 3656900, with gold heat sink and a white paint dot, replaced earlier ECUs as Chrysler improved the circuitry for better cold starting in low temperature conditions. As a running change in 1973 production, a radio noise suppression capacitor was added to the external wiring, connected to the green wire with red tracer.

In early 1974, ECU part number 3755550, with a gold heat sink, which now included the radio noise suppression capacitor internally, was released. Later in 1974, part number 3874020, with added voltage spike protection and a gold heat sink, replaced earlier ECUs. 3874020 was used through 1979.

In later 1975 production, Chrysler adjusted the primary resistance in the dual ballast resistors to 1.25 - 1.5 ohms and also encased the resistor reducing the thermal action as part number 3874767. The effect of current limiting based on engine speed and temperature variation was lessened to a shorter effective range. Although the actual resistance specification changed, much of the literature specification did not.

The 1.5 ohm dual ballast resistor used in 1975-1979 ECU applications should not normally be used in place of the 0.5 ohm dual ballast resistor used in 1971-1975 ECU applications. The later dual ballast resistor will function okay in place of the earlier dual ballast, but depending on the ECU, optimal coil energy will be reduced.

In 1976, Chrysler introduced Electronic Lean Burn (ELB) which replaced the ECU in many applications, although the ECU function was integrated into the ELB Spark Control Computer (SCC) as the internal Ignition Control Module (ICM) in conjunction with the Program Schedule Module. ELB initially used a dual ballast resistor with the five ohm side connected to the SCC and the 0.5 ohm side still connected as ballast resistor for the coil. The conventional ECU with dual ballast resistor continued to be used in non-ELB applications.

In 1979, ELB was revised with digital control in the Program Module and the extreme lean condition of ELB was dropped. The revised SCC was called Electronic Spark Advance (ESA) or Electronic Spark Control (ESC). The conventional ECU with ballast resistor continued to be used in non-ESA/ESC applications. The ECU and ballast resistor was unchanged but the coil, part number 4167126, 4176009, et.al. was revised. The secondary wire connection was changed to an internal male lock terminal and primary resistance is a nominal 2 ohms.

In 1980, Chrysler revised the non-ESA/ESC five pin ECUs to remove the external auxiliary resistor connected to the fifth pin of the ECU. The external resistor function is included internally in the revised internal circuitry. This new unit for 1980 is the "four pin" ECU, part number 4111850, which was used through the 1980s. The new two terminal ballast resistor (part number 4106340, 5206436, et.al.) is 1.25 ohms ( 1.12-1.38 ohms ) for the primary circuit to the coil. The new ballast resistor eliminated the metal bracket and had a mount molded into the ceramic housing.

Stock ECUs and coils require ballast resistors as previously described. The high performance and racing Direct Connection/Mopar Performance ECUs typically require a primary ballast resistance from 0.25 ohms to 0.8 ohms depending on the ECU version and coil. Early Direct Connection/Mopar Performance ECUs had five pins and required dual ballast resistors, and later ECUs had four pins and used single ballast resistors, following the similar changes in production ECUs.

Summary of Chrysler Production ECUs​

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ECU Part Number	Usage	Pins	Ballast Resistor	Coil	Notes
3438850	1971-1972	5	3656199	2495531	1971 - 340 manual transmission only. Black case, gold heat sink.
3656127	1972	5	3656199	2495531	400 & 440 HP manual transmission, engine speed limited. Black case, red heat sink.
3656128	1972	5	3656199	2495531	340 manual transmission, engine speed limited. Black case, blue heat sink.
3656900	1973	5	3656199	2495531	Improved cold starting. Black case with white dot, gold heat sink.
3755550	1974	5	3656199	2495531	Added radio suppression capacitor. Black case, gold heat sink.
3874020	1974 - 1979	5	3656199 to mid 1975, then 3874767	2495531	Added voltage spike protection. Black case, gold heat sink.
4111850	1980 - 1991	4	4106340, 5206436	4176009	Four pins, two terminal external ballast resistor. Black or blue case, gold heat sink.

Summary of Chrysler High Performance ECUs​

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ECU Part Number	Pins	Usage	Coil	Ballast Resistance
3438850R	5	Modification of production ECU for NASCAR racing up to 7000 RPM, or 8000 RPM with different coil and ballast resistor	Production or similar coil, 1.3-1.8 ohms. Or higher output with a racing coil.	0.5-0.7 ohms. Or other resistance to match the coil used.
P3690011	5	First performance parts ECU for Super Stock, etc. Replaced 3438850R.	Production or similar coil, 1.3-1.8 ohms to 7000 RPM. Or higher output racing coil to 9500 RPM.	0.5-0.7 ohms. Or other resistance to match the coil used.
P3690256	5	High RPM ECU for Super Stock, etc. Replaced P3690011. Blue with gold heat sink.	Production or similar coil, 1.3-1.8 ohms to 7000 RPM. Or higher output racing coil to 9500 RPM.	0.5-0.7 ohms. Or other resistance to match the coil used. Use Accel 150001 per Accel instructions with 140001 Super Coil.
P3690256A	5	Revised P3690256.	Production or similar coil, 1.3-1.8 ohms to 7000 RPM. Or higher output racing coil to 9500 RPM.	0.5-0.7 ohms. Or other resistance to match the coil used. Use Accel 150001 per Accel instructions with 140001 Super Coil.
P3690256B	5	Revised P3690256A.	Production or similar coil, 1.3-1.8 ohms to 7000 RPM. Or higher output racing coil to 9500 RPM.	0.5-0.7 ohms. Or other resistance to match the coil used. Use Accel 150001 per Accel instructions with 140001 Super Coil.
P4007298	5	Released in 1978 to replace P3690256/A/B. Chrome with a blue multi-fin heat sink.	Production or similar coil, 1.3-1.8 ohms to 7000 RPM. Or higher output racing coil to 9500 RPM.	0.5-0.7 ohms. Or other resistance to match the coil used. Use Accel 150001 per Accel instructions with 140001 Super Coil.
P4120505	4	Released for general high performance and moderate race applications. Orange with blue heat sink.	Production or similar coil, 1.3-1.8 ohms to 5500 RPM.	0.5-0.7 ohms. Or other resistance to match the coil used. NOTE: later ballast resistor ~1.2 ohms can be used. Use Accel 150001 per Accel instructions with 140001 Super Coil.
P4120534	4	Released in 1980 to replace P40007298. Chrome with black heat sink.	Production or similar coil, 1.3-1.8 ohms to 6000 RPM. Or higher output racing coil. 10500 RPM with P3690560 coil.	0.5-0.7 ohms. Or other resistance to match the coil used. P2444641 0.25 ohm with P3690560 coil.
P4120600	4	Released in 1981 as a high RPM, racing only unit which can sink more current to drive the coil. Gold with black heat sink.	Works with production coil to 5500 RPM, but not recommended. Use P3690560 coil or similar to 10500 RPM.	Resistance to match the coil used. 0.5-0.7 ohms with production coil. 0.8 ohms with Accel Super Coil. Use P2444641 0.25 ohm with P3690560 coil.

​

Summary of Chrysler Production Ballast Resistors​

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Part Number	Usage	Terminals	Ohms	Notes
1689336	1957 - 1959	2	0.5	Screw terminal block and pigtail.
1889545, 2010000, 2095262	1956 - 1961	2	0.5	Metal case. Terminals: one spade, one screw.
2095501, 2196316, 2275590, 4106140, CH452	1960 - 1972	2	0.5	Metal strap, although some later manufacture might be with a molded mounting hole. Open back, although later issues such as 2275590 and 4106140 might be sealed back.
2444641	1964 - 1968	2	0.25	Used with Prestolite transistorized ignition. Open back.
3656199, CH455	1971 - mid 1975	4	0.5/5	Open back primary resistor. Sealed back auxiliary resistor.
3874767, CH456	Late 1975 - 1979	4	1.25/5	Sealed back for both resistors.
4106340, 5206436 CH458	1980 - 1989	2	1.25	No metal strap. Sealed back. Some listings show 5206436 as 1.0 ohm. Others show it as 0.7 ohm.

Summary of Chrysler High Performance Non-Production Ballast Resistors​

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Part Number	Usage	Terminals	Ohms	Notes
P2095501	Direct Connection/Mopar Performance	2	0.5	Reissue of the original 2095501. Open back.
P2444641	Direct Connection/Mopar Performance	2	0.25	Reissue of the original 2444641. Open back.
P5206436	Direct Connection/Mopar Performance	2	1.25	Some listings show as 1.0 ohm. Others show it as 0.7 ohm.
P4529795	Direct Connection/Mopar Performance	4	1.25/5	Replacement for 3874767.

 

[MoPar~Man]

Any ideas what the dual-resistor ballast 3874746 was for (year, make/model, engine, etc) ? I have one, don't know where I got it. It's a fully potted 1.25 / 5 ohm resistor. The dual ballast that was on my '73 Satellite / 318 is identical to this 3874746, but it has absolutely no marks or numbers stamped into it.

I think what you're saying is that, for '73, the expected ballast would contain a 0.5 ohm resistor, paired with a 1.8 ohm coil (the actual P/N on the coil doesn't really matter?).

 

[Vaanth]

Any ideas what the dual-resistor ballast 3874746 was for (year, make/model, engine, etc) ? I have one, don't know where I got it. It's a fully potted 1.25 / 5 ohm resistor.

The information you ask about is in my prior post, but specifically, 3874767 was equipped on late 1975 - 1979 all non Electronic Lean Burn or non Electronic Spark Advance domestic rear wheel drive car and light truck applications.

The dual ballast that was on my '73 Satellite / 318 is identical to this 3874746, but it has absolutely no marks or numbers stamped into it.

The unmarked resistor is likely an aftermarket replacement for 3874767 or 3656199.

I think what you're saying is that, for '73, the expected ballast would contain a 0.5 ohm resistor, paired with a 1.8 ohm coil (the actual P/N on the coil doesn't really matter?).

This information is also summarized in my prior post, but in general, the part number does not matter. Select the coil and other components for direct current limiting based on the resulting cumulative resistance. The cumulative resistance of the primary circuit including the ballast resistor, the coil primary winding, the wiring, the connections, and the effective junction resistance of the switching transistor or contact point resistance, should be such that the direct current (neglecting dynamic impedance factors) is less than or equal to the capacity of the series connected components, under the applied primary voltage. Depending on the applied voltage, primary current should be kept at four to six amps, with spikes less than 10 amps for production ECUs, or three to four amps with spikes less than six amps for production contact point sets.

For estimating purposes, the coil and ballast resistor are the primary resistances to consider. With good wiring and connections, their resistance is negligible. For these same purposes, the effective resistance and voltage drop across the transistor, and the resistance of healthy contact points can be considered to be zero.