Correct ballast resistor for standard to electronic conversion

[MoparGuy68]

Before I continue with my Charging issue thread, I'd like to know which type of ballast resistor should be on my car. Being a 1971, my car would have come from factory with standard ignition and a single style ballast resistor. It has been converted to MOPAR electronic ignition, and has a single style ballast resistor.

The 1972 & 1973 Factory service manuals that I have, show the electronic ignition using a DUAL ballast resister. When I converted my 1971 Challenger from standard to electronic (back in 1989), I apparently still ran a single ballast resistor. I had to look at an old photo from 1998 to confirm this. I also never had any electronic issues with that car. As I recall, the ammeter gauge had already been bypassed before I bought it and I left it that way.

When converting a standard car to electronic, should a SINGLE or DUAL ballast resistor be used? The guy that shortened and re-flared my fuel line said I should be running a DUAL resistor with the electronic ignition, but I never did that with my Challenger. So is he correct or not?

 

[Nacho-RT74]

Dual ballast is for 5 pins ECU modules
Single ballast for 4 pins ECU modules

The missed pin was destined to take the external secondary power source from the extra ballast resistor. Not anymore needed when the engineering department moved out this source internally to the ECU ( I think on earlier 80s? )

You can use a 4 pins ECU into a dual ballast resistor setup, just the secondary power source won't go anywhere. It shouldn't be used the other way around because won't work propperly ( or simply won't work )

 

[wish4hemi]

Dual resistor is only required if you’re running a 5-pin ECU (unlikely).

 

[moparedtn]

The Mopar electronic ignition conversion kits came with a single ballast from Ma herself.
'Nuff said.

 

[66Satellite47]

Which box is it? If Mopar which part #?

Edit: If Mopar Orange box single ballast either .5 or .7 Ohm or .8 Ohm with Accel coil

 

[whyjay]

Just did the electronic conversion on my 71 Charger. The kit included a single ballast. I believe any new ECU will be four pin.

 

[HALIFAXHOPS]

Really depends what box you are running actually. Hope this helps.

Most use the 1.2 ohm ones. Check the value if you are using the single one. They can not be 1.2 They also have them in other values. You can see that in the chart.

 

[RJRENTON]

Really depends what box you are running actually. Hope this helps.
View attachment 987637
Most use the 1.2 ohm ones. Check the value if you are using the single one. They can not be 1.2 They also have them in other values. You can see that in the chart.

IMO....
The ORIGIONAL ballast resistor used with points ignition was 0.5 ohms. When Mopar introduced the electronic ignition in 1973 (?), they used a DUAL ballast resistor of 5.0 ohms AND 0.5 ohm values. The connection to the resistor was origionally a dual plug. The 5.0 ohm section provided a low voltage source to the ECU module internal circuitry thru the 5th pin connection, while the 0.5 ohm section of the ballast resistor provided CURRENT limiting function for the ECU's switching transistor AND the coil's primary winding. Later, as we all know, the ECU was modified to eliminate the 5.0 ohm section of the ballast resistor and the ECU's 5th pin connection and its internal circuitry modified to operate at the full 12 volt ignition supply from the switch
Subsequently, the newer electronic ignition conversions use a ballast resistor of ~ 0.7 ohms, to limit switching current to the ECU's switching transistor AND the coil's primary winding current.
I believe, because of the ECU's point of manufacture, inferior internal components were used, and MAY account for numerous reported failures AND possibly the substitution of "higher output " coils, in search of more horsepower, by unassuming owners, are to blame. The ignition system needs to have omponents that compliment each, other of the same manufacturer, to reasonably assure compatibly resulting in smooth operation and long life. Just my opinion of course.
BOB RENTON

 

[66Satellite47]

Bob, thanks for explanation. At least Mopar was fairly clear that the ignition components needed to match each other as indicated by the chart in post#7. They also made it clear their MSD units needed the proper coil. There is another chart in one of the newer Bibles that has some newer recommendations with some different parts, with some other resistors.

 

[MoparGuy68]

Thanks guys. My Challenger had the Orange ECU box so it had the 4 pins, which matches the single resistor I had on it.

The Super Bee has an unidentified 4 pin ECU box on it, with a single resistor. Don't know who made the box. Don't yet know what the resistance is on the installed resistor.

The car came with a lot of extra parts. There is an older Orange box that was made in USA. Also have another 5 pin box that is marked WELLS 1290E24. Four ballast resistors: two dual and two single. The singles are marked .8 OHMS and look different than the single that is mounted on the car. The duals are unmarked and I've not tested any of them. All extra resistors are the closed back type.

The engine harness ECU plug has 5 female connectors on it. I assume ALL electronic engine harnesses have 5 female connectors?

 

[RJRENTON]

Mopar's origional 0.5 ohm resistor was open on the back side. The aftermarket resistors are usually filled with with a ceramic compound, sometimes manufactured by Dale, are prone to premature failure due to overheating of the nichrome resistor element. Although I use a Prestolite dual point distributor, Mopar 0.5 ohm resistor and NOS Mopar coil, i still carry an origional 0.5 ohm open back resistor as a "just in case" spare. The $$$ between an oem type ballast resistor and an aftermarket resistor is negligible....just get the correct one for your application
My opinion,.....pitch out the dual resistors and the 5 pin module or send them to Nacho. Ask Halifaxhops if he could test your origional appearing orange box and if bad, purchase one of his units.
BOB RENTON

 

[66Satellite47]

So many ECU's out there & we don't have any real idea of how well they work for a performance application or what the reliability is.

 

[Bee1971]

Or where you can buy these 5.0 Ohm / .5 Ohm Dual ballast resistors ?



‘All the ones I measured are 5.0 Ohm / 1.2 Ohm Dual ballast
Standard RU12

Standard Single ballast is .5 Ohm
Standard RU11

Standard Single ballast is 1.7 Ohm
Standard RU4

 

[HALIFAXHOPS]

I can test your ecu just the rides. Easy with a bench tester.

 

[66Satellite47]

Mopar's origional 0.5 ohm resistor was open on the back side. The aftermarket resistors are usually filled with with a ceramic compound, sometimes manufactured by Dale, are prone to premature failure due to overheating of the nichrome resistor element. Although I use a Prestolite dual point distributor, Mopar 0.5 ohm resistor and NOS Mopar coil, i still carry an origional 0.5 ohm open back resistor as a "just in case" spare. The $$$ between an oem type ballast resistor and an aftermarket resistor is negligible....just get the correct one for your application
My opinion,.....pitch out the dual resistors and the 5 pin module or send them to Nacho. Ask Halifaxhops if he could test your origional appearing orange box and if bad, purchase one of his units.
BOB RENTON

Bob, BTW my dual resistor 35656199 both .5 Ohm has the ceramic fill. The single .5 Ohm 2095501 is open. Both of these came with my Blue box 3690256 conversion kit. That kit really works, although they didn't recommend it for street use/below 2000 RPM for extended periods. Does good job past 7000 RPM. 5 pin.

 

[RJRENTON]

Bob, BTW my dual resistor 35656199 both .5 Ohm has the ceramic fill. The single .5 Ohm 2095501 is open. Both of these came with my Blue box 3690256 conversion kit. That kit really works, although they didn't recommend it for street use/below 2000 RPM for extended periods. Does good job past 7000 RPM. 5 pin.

IF your ECU orange box has performed well, to your satifaction, with the open back 0.5 resistor, and suggested coil, this is the combination to stick with. The 5 pin ECU and the corresponding dual ballast resistors should be disposed of to not be used down the road. The 5 pin ECU and dual element ballast resistors are an obsolete design and are not serviced separately, unless thru some eBay vendor, or IF you are interested in an origional appearing car, IMO....just get rid of those items.
BOB RENTON

 

[66Satellite47]

IF your ECU orange box has performed well, to your satifaction, with the open back 0.5 resistor, and suggested coil, this is the combination to stick with. The 5 pin ECU and the corresponding dual ballast resistors should be disposed of to not be used down the road. The 5 pin ECU and dual element ballast resistors are an obsolete design and are not serviced separately, unless thru some eBay vendor, or IF you are interested in an origional appearing car, IMO....just get rid of those items.
BOB RENTON

Bob, Ya mine is a Blue box, obsolete, but better than any Orange box. Kept using the Blue box as an in place spare to my MSD 404BC. Mine were drag cars no intent to look original. Not fancy, just really fires the plugs. Sorry, BTW I'm not the OP or the other Orange box guys.

 

[Daves69]

....Ya mine is a Blue box,.....

Is that a P3690256?

 

[RJRENTON]

Is that a P3690256?

To be absolutely assured and definitive of which ECU (blue vs orange box) is better, I would want to see a schematic diagram of the internal components and connections. This is NOT how the ECU, resistor, coil, and distributor pick up coil is connected BUT what is inside the ECU box. I'm sure my request would be ignored by the manufacturer unless l could perform a autopsy of a failed box and determine a root cause failure analysis.
BOB RENTON

 

[Geff McCarthy]

I have an aftermarket orange module, the product literature requires a 1 ohm resistor.