Finishing restoration on a 70 Challenger T/A. My question is what ballast resistor to use. I converted to electronic ignition and the harness is set up for a single resistor. I know that there was a single used ith points like the car came with and there was a later design used on electronic ignitions. Is there an Ohm difference? Does the dual resister have a start and a run resistance and is that not necessary? Gerry.

The MP dist comes with the correct resistor.I believe it is about 1.2 ohms.No need for a dual resistor.That was used in later apps.One for a 71 should be single and work.Rocky

as Rocky said, a 1.2 will work fine provided your conversion was the MP conversion kit.

Might peruse the "ballast resistor bypass" thread on page 2 (has over 50 comments!). Yes the MP ballast for the chrome/orange box has a nominal ohms listing of 1.25 ohms but may (& probably will) vary from that (new or used) a certain amount and you do have a fair amount of leeway. Carry a spare ECU/ballast in the glove box!

yeah, i was involved in that one over a year ago. i finally gave up as i couldn't get my point across about the ballast lowering the current which lowers the heat inside the units. i kinda shy away from these ballast posts now. sorry OP, didn't mean to hijack!

Saw the other post. WOW hot debate! I believe I understand now. Thanks, Gerry.

if you want your CAr to be correct use the points style BR. It has 1.7 ohms. That's what I use on my t/a with electronic ignition and I have no problems.

It all depends on what ignition componets you are running. It also depends on if you read the information on those parts, and not go off of what somebody said years ago that might apply if you were running the specific pieces they are referencing.