4 to 2 Prong Ballast Resistor Change - 72 340

Hi Everyone,

I am finishing up the electrical in the engine compartment and I have a question about the new 2 prong style ballast resistor. I know that the original set up for my 72 Roadrunner was a 4 prong ballast resistor but the kit I bought from summit (SUM-851003) https://www.summitracing.com/tx/parts/sum-851003/replacementparts/make/dodge?prefilter=1 has a 2 prong. Do I need to cut wiring harness to fit over the 2 prong or can I just plug it in even though it has the extra 2 wires? I think the kit came with the wires to do as much but I was not sure and which wires to cut. I also thought I read some where people drill out the back of the 4 pronged ones so it looks original but functions like the 2 pronged one? I am open to doing that as well.

I am sorry if this is a dumb question. This is my first time working on the ignition of these cars and I am not familiar with it. I appreciate all help.

*edit* I also bought several 4 pronged units thinking I needed them well before I got the distributor. If I can use those and be fine I will be glad to do that too.

this is the only difference




but you can keep the 4 ballast resistor and wiring with a 4 pins setup... just green traced red wire won't get anywhere on ECU.

4 pins ECUs didn't get the secondary voltage source coming from ballast but moved inside this source

If it doesn’t matter to u , u can splice the wires together on each side of the resistor then use the 2 prong restrictor. Kim

no need to splice the green traced red, just not use it if he wish to replace the ECU pigtail for the new harness... or if engine harness is still in good conditions, just keep it like it is

Agree, no need to cut or splice anything. See picture. Here is some reading material on 2-pin vs. 4-pin ballast about a 1/4 of the way down the page.

https://moparconnectionmagazine.com...-road-runner-with-yearone-and-mancini-racing/

If you want a stock look, do what Nacho suggested, and use the four pin ballast. You don't have to do anything to it, a four pin ECU will work perfectly with it.

Thank you all, I am extremely grateful for the help. I bought a brand new oem style harness and will probably do as Nacho suggested and use a 4 pin ecu. Thanks again, I have a lot to learn about electrical!