I've got and MP distributor and a chrome box with a 45 year old stock 318 coil (not on a 318 though). I bought a Petronix flamethrower, with 1.5 ohms, resistance coil. Do I still need the ballast? Or can that coil see 12 volts all the time? I thought I've read that the ECU doesn't like 12 all the time either. I'm really clueless here.

Pertronix coils have internal resistance and do not need a ballast. That much I know.

The Pertronix coils are made for full 12V so the coil will be fine and with 1.5 ohms I believe the ECU can switch on/off the amount of primary current that you'll have with 1.5 ohms resistance. I'm running an FBO coil with a MP .25 ohm ballast triggered by an OEM ECU & it starts instantly/runs flawless & iirc the (measured) pri ohms of my FBO coil was .8 ohms so I'm passing more primary current on my setup than you would be plus you're running a hotter box than I am but with that being said it's always a good idea to carry spares in the glove box . EDIT I was thinking that OE points coils like your 45 year old one had 1.5 ohms & later electronic ones had .5 ohms but I may be backwards on that & the actual ohms will likely be somewhat different than the nominal listed ohm spec

Well, then could I take apart the resistor and put an 8 or 10 ga wire in place of the resistor itself and reinstall it for appearance?

Just my .
Mopar production has a 1 ohm resistor that I believe will work just fine with the chrome box and the flame thrower. Part number 5206436.

If the coil can take 12 volts, but the ECU can't, could I then just bypass the ballast for the coil but leave it wired over to the ECU? Or does power go from the coil to the ECU too? I'm just trying to learn here.

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If the coil can take 12 volts, but the ECU can't, could I then just bypass the ballast for the coil but leave it wired over to the ECU? Or does power go from the coil to the ECU too? I'm just trying to learn here.

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The ballast resistor is there for the coil. If Pertronix comes with a 1.5 ohm resistor with the coil, then I would think it is needed. I would not think that the coil will handle a full 12volts +. The exception would be if used with an ignition system such as MSD where the resistance is built into the unit.

The petronix does not come with a external resisitor. It is built with 1.5 ohms of resisitance in it. It is designed for a full 12 volts.

If that's true then I would think that you could run a full 12 volts to the coil and by-pass the ballast all together. I'd run the engine for a while and periodically check the coil for excessive heat. If it doesn't get HOT then you should be "good to go".

Many people do not understand the task of the ballast resistor..
Certain newer coils do not require a ballast resistor, they either have it built-in or are designed to handle the higher input voltage. The purpose of the ballast resistor is to protect the coil from higher current rather than voltage as the resistor heats up its resistance increases which decreases the current to the coil..

Just my $0.02....

Well then, is there even a benefit to not run the resistor to the coil?

Not being smart but it seems a post like this comes up about once every few months and the poster gets many different answers that can really confuse them. I believe one of the Mopar mags about 6 months or so ago ran an article and said basically any Mopar electronic ign will work fine without using a ballast resister and told everyone to pretty much throw away your ballast if you have electronic ign meaning no points. At least thats the way I heard it. I know I started racing muscle cars in the early 70's and most still had points then. I also know I saw a few guys burn up the chrome MP ecu by using the wrong or no ballast or the wrong coil and I saw a few coils go bad. In fact MP had a section in their eng book on what ballast to use with the different ecu boxes they had out there in use. And to this day it still seems to confuse many.

Do I understand this right as the original poster here is using a MP ecu and bought a Petronix coil to use with it ?? I am guessing you are using a MP dist ? Honestly my best advice would be to either go on the Pertronix website or call their tech line and talk to them and tell them just what you have and see what they recomend since it is their coil and they designed it. No matter how much we tell you we are not the engineers who made it and if we tell you wrong you will be the one on the side of the road with a burnt up coil or ecu. Like I said I dont mean to sound like a smart a$$ as I can also tell you what I recomend but myself I have not used that coil ever on my cars.
Bottom line is the current will go thru the coil and thru the ecu to ground so the wrong current could damage either one. Your ecu will turn the primary circuit on and off but what ever current flows in the system (2 amps or 6 amps) will flow thru the coil and the ecu and can burn up either if its not right. If you use the wrong or no ballast you may burn the coil or ecu up. We can tell you to run no ballast or a .25 ballast or a 1.5 ballast. Many will work but you want the setup that will keep working and not damage any of the parts.

My advise of course is carry spares to be safe and call Petronix and get their advise. Ron

That resistor will save your ignition box from melting the epoxy from the back side of it,i know this for a fact!!This car was running and driving for years until....
Had a stumble above 5500 rpm removed ballast, stumble gone problem fixed.
Week later cruze night car quit,open hood black ooooz running down the fire wall.
Had a dizzy problem causing the stumble.Replaced the dizzy and the box,installed a new ballast.

Run the ballast resistor,it is there for a reason