Ok thank you. I’m sure mine came with the orange w/ blue and my resister is a 1.2 that came with the distributor
Ignition module
- Thread starter Genes 340
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Do you trust these? Otherwise I found the orange one on e bay brand new in the box
Vaanth
Well-Known Member
In general, the Wells ECU should work fine with your distributor, at least for basic operation. It is a direct replacement for a production ECU. The original Direct Connection/Mopar Performance distributors were just selected production distributors with a modified advance curve, via spring change. Later, the distributors were outsourced to Mallory with a different design, and then other suppliers entirely.
The P4120505 orange ECU is rated to 6000-6500 RPM, depending on the other components, but 5500 RPM in the system with the stock coil. The production ECUs, except the 1972 limited versions, are rated to 6000 RPM for the ECU itself, but 5500 RPM in the system with the stock coil. These ratings are for the original and earlier production parts. New versions are probably rated the same, but less likely to match the ratings, and unlikely to match the reliability.
The Wells ECU will be no better at high RPM than a stock ECU, but should perform similarly otherwise. It will be less maximum RPM than a P4120505 orange ECU and likely less stable as it nears its RPM limit. The Wells ECU finish is more nickel than chrome. These and other aftermarket ECUs that look chrome are not the same as the Chrysler "chrome ECU" which is rated higher. These regular replacement ECUs regardless of case finish are rated the same as stock production. There are some specialty aftermarket ECUs that do claim higher RPM ratings though. The following image shows an actual Chrysler chrome ECU, number P4120534, on one of my cars:
I have been running this since the 1980s, but with a 0.5 ohm (earlier) or 1.2 ohm (currently) ballast resistor and 1.4 ohm Accel 8140 coil, so RPM is limited from the rated maximum. I originally converted to electronic ignition, wired, and ran the P4007298 ECU on this car in 1979.
Ray listed the published ratings for the Chrysler chrome ECU (P4120534) and others, but the information is also in my following table:
| 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. Or higher output to 6500 RPM with racing coil. | 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 with racing coil. 8500 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. |
Note that some ratings varied a little over the years.
For the Wells replacement ECU, or a P4120505 orange ECU, your ballast resistor should be 0.5 - 1.5 ohms, and your coil should be 1.3 - 1.8 ohms. Resistance at the lower end of the range for the resistor and/or the coil will allow a little more delivered spark energy, but anything in this range will function properly. DC resistance matching is not the only consideration in the dynamic ignition system, but it is the starting point for matching components.
If the tachometer read correctly with the previous ECU, but not the Wells ECU, double check the tach wire connection and routing of the wire. The wire should not be near, or run parallel to, any secondary ignition (spark plug) wires. It's also best not to run the tach wire directly parallel to the coil negative lead. If everything otherwise checks out or if swapping the ECU corrects the issue, the Wells ECU may be generating too much noise from the transistor switching at higher RPMs. Clean enough to operate the ignition system, but just noisy enough to cause the tachometer issue. In this case there is not much that can be done to keep the ECU and same tachometer, but there are possible filter circuits to put in the tach lead that might help. Tachometer signaling, especially if originally designed for contact point switching, can be falsely triggered by the ECU switching, if noisy, and lead to erratic or inaccurate readings.
Yes the tach worked fine with the orange w/blue until it lost its filling under the module. Then I put that wells on and the tach wouldn’t go over 2500 rpms and then got erratic and then cutting out at high rpms. Should I go with the orange with the blue that I found on eBay that’s brand new or use the hirev 7500 that jegs offers? I also have a accel super coil from the 80,s that I’m using
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Vaanth
Well-Known Member
If the "orange with the blue" is a genuine, USA made, P4120505 ECU, then yes, recommended. If it is a modern version, or one of its orange imitators, I can't recommend it. I also can't recommend the Jeg's offerings or anything else made in recent years. However, if that is all available to you, check around for more specific information on that specific ECU.
Note that the Accel Super Coil is specified to use the Accel 150001 0.8 ohm resistor in series with the stock (or equivalent) ballast resistor. It can work without it though depending on the ECU, etc.
If the ECU is causing higher RPM cutting out, it may be getting over-driven with the Super Coil. Try adding the correct, or similar, 0.8 ohm ballast resistor if it is not already being used.
If the ECU is being over-driven, the added resistance might help with the tach issue too. The P4120505 ECU can handle more current, so that might be why it did not have trouble with the tach, but the Wells ECU does.
Accel Super Coil instruction is attached as FYI if needed.
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Ok thank you so much for your help. I think I see my problem now and yes it is a genuine orange/ blue.i do have two ballast resistors on the car. The original one and the one that came with the distributor hooked up. So my problem was probably putting on that wells module. I didn’t realize there were different ones. Thanks again everyone that was involved in this matter
Those are good units.
Probably one of the new MP authorized kits made overseas. I will not touch those kits unless they are made pre 2000
A few times I have had a oem ECU that also puked ts guts out and still worked fine. I did carry a spew new one in the glove box.
The guts is insulation /waterproofing I figure.
Yea I think so too. But mine quit working after that. It did last 40 years though on a good note
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