Moparts Tech Archive
4 or 5 pin ECU?4 or 5 pin ECU?
Hi guys. I just bought a wiring harness for the 71 340 Cuda. It has 5 wires going to the ECU plug. Can I just use the orange box with 4 pins and be just fine? Or do I need to get a 5 pin ECU? Thanks a lot.
To my knowlege, either one will work. It won't hurt anything in the electrical if you try it and it doesn't work. It SHOULD work fine, though.
4 pin will work fine. Install it and enjoy! Ron
Even the MP conversion kit, which come with a 4 pin orange box, comes with a 5pin wiring harness. One wire is left unused. You'll be fine.
Wire it and fire it, then go admire it!!!
4 pin superceeds the 5 pin brain and can be used in place of the 5 pin. The 5 pin has a separate start circuit thus the reason for the dual ballast resistor. The 4 pin combines the start run circuit and if used in replacemnet of the 5 pin uses only the run side of the dual ballast resistor. The 4 pin system uses only a single ballast resistor.
kinda old topic but I just saw it now... I also bought a new orange ECU for my 72 Roadrunner with elec. ignition and this one has 4 pins, although my old ECU had 5 pins! (and is black). I got also a double ballast resistor!
The 4 pin replaces the 5 pin ubit and will use the run side of the dual ballast resitor. Your 4 pin should work fine. The run side of the dual ballast is very close to the same ohm reading as the single ballast resistor. In fact when a dual ballast resistor burns out on the start side the wires on each end can be wired together and the car will run fine on the other side.
Run the 4 pin on either 2-4 prong ballast as stated above, do not run 5 prong with a 2 prong ballast the car will not run properly. A number of years ago Chrysler was selling 5 prong control boxes with 2 prong ballast resistors, this is the wrong setup
You can wire all 4 wires together and the car will run. That is esendially wat the 4 pin does, it elimates the start side and combines the start run to one circuit instead if a low resistance side fro start and low higher resistance side for the run side.
I see... hmm does anyone has a scematic of the ECU itself? Wondering how that really works!
Yes 72 with original electronic ignition would have had the 5 pin. the 4 was later update. Can't remember the year but 74 or 5 I believe.
Oh.. so you can't get the original black 5pin ECU's anymore?
Didn't know about the different functioning of the 5-pin type ECU's & the purpose of the dual-element ballast resistor - learn sumpin' new everyday on Moparts.com! Anyway, it would seem to me that you could mimic that function using a commonly-available 4-terminal type relay to bypass the resistor when cranking, or route the current through a lower-rated resistor, for a hotter spark while cranking.