Ballast resistor for MSD?
MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
Senior User
Joined: Aug 2004
Posts: 389
Likes: 0
From: Nassau Co. NY
MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
This seems to be an argument over semantics rather than technical content, but in my original post, I directly answered what was essentially a yes or no question with no assumption about existing wiring. Half the people who come to this forum with ignition questions are doing so because they're working with something that doesn't work or has been modified.
Is it required? Yes. Is it part of the original harness? Of course, but that wasn't the question. Only until asked specifically how to implement this piece did I go into further detail, which was made explicit:
It's part of the original wiring harness because it is required. You are of course not required to add one if you already have it as part of your original wiring, but I can't assume that's what this individual is working with right off the bat. Instead, I start off stating the facts, and leave it upon the individual asking the question to understand how their setup differs from what I have described (with my guidance as needed). Your style of answering the question would have been just as acceptable for me too; it's simply different than mine.
Is it required? Yes. Is it part of the original harness? Of course, but that wasn't the question. Only until asked specifically how to implement this piece did I go into further detail, which was made explicit:
It's part of the original wiring harness because it is required. You are of course not required to add one if you already have it as part of your original wiring, but I can't assume that's what this individual is working with right off the bat. Instead, I start off stating the facts, and leave it upon the individual asking the question to understand how their setup differs from what I have described (with my guidance as needed). Your style of answering the question would have been just as acceptable for me too; it's simply different than mine.
Fleet Mechanic
Joined: Aug 2010
Posts: 1,574
Likes: 6
From: Cranbrook, Ont., Canada
X2 on that fmc400. I have a 77 with the duraspark2 ignition and I bought a MSD blaster 2 coil. The speed shop said I needed a ballast resistor to go with it. I disagreed cause I already had one with the stock ignition. We agreed to disagree. In the long run I was right and NO problems. I understood what you were trying to explain and why.
Senior User
Joined: Aug 2004
Posts: 389
Likes: 0
From: Nassau Co. NY
All I am saying is if someone who is obviously not familiar with a topic asks "Do you have to have a resistor?" and you answer "yes" they will most likely install it with the MSD which leads to added expense and work because you answered the question with a black and white answer. Then again I live in the grey area so what do I know.
MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
It's bundled in the dash harness, with the words "DO NOT CUT OR SPLICE" stamped along its length. It's usually RED or PINK. In lieu of searching for it, you can check for it electrically in the case of Duraspark II. Turn the key to RUN and measure the voltage at the positive (BATT) terminal of the coil. If it's 6 to 7 volts, the resistor is there. If it's 12 volts, the resistor is not there. Measure the voltage at the same place with the coil disconnected and it should jump up to 12 volts.
Laughing Gas
Joined: Jan 2012
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MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
Agreed, sounds like you're powering it from the factory ballast resistor. Nice work on the measurements.
You can check for gross failure of a coil by measuring the primary and secondary winding resistances. Between the two smaller terminals you should see about 1 ohm (not counting meter lead resistance). Between either small terminal and the large center terminal, you should see between roughly 7 and 11 Kohms.
You can check for gross failure of a coil by measuring the primary and secondary winding resistances. Between the two smaller terminals you should see about 1 ohm (not counting meter lead resistance). Between either small terminal and the large center terminal, you should see between roughly 7 and 11 Kohms.
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