Help Chase A Weak Spark (Coil Voltage)

Ideally you'd want no less than a several tenth(s) drop from your reading at the batt posts as you get at the coil positive pri terminal and a nearby ground such as the intake manifold both while "cranking" & you can get by w less if it's not a cold weather situation as there you need all the power you can generate. In "run" you have too much ohms in the ballast which is making too much voltage drop. The nominal ohms in the ballast supplied w the orange/chrome ECU's is 1.25 ohms and most are actually higher than that & you can go less than 1.25. #1 is what coil do you have as that primarily sets the ballast requirement though a particular ECU can only switch so much current

Sorry for the delay, but I have been kind of going solo
on this the past few days. Thanks for all, this one really
has me

1970 Roadrunner 440.

I checked all my connections & find nothing wrong. Chased what
seemed like a whole lot of nothing as everything far a I see is right.

I agree with less resistance at the ballast in "run"...
except for one thing. In "start" I should still see
12+ volts to the coil & I only am getting 8.
When I disconnect the "run" side of the ballast resistor,
hold the key in "start" with 2 extensions & a 3/8 deep socket
(wedged from the floor), I get full 12+ volts to the coil.

My ballast may be high and will order a few 1ohmer's, butI believe
it's something pertaining to the resistor, or the "run" side
of the resistor... which would include the ECU.

Also, with the "run" side of the ballast hooked up, the plug (see below)
does not fire in start or run, but does fire when I return the key
to the accessory position. With the "run" side of the ballast disconnected,
the plug fires in "start" as it should.

In case I did not mention, The number one cyl is in the fire position and I have
the #1 spark plug clamped to ground so I can watch it fire from in the car.

No this weak spark has plagued me since the rebuild.

Keep in mind that I disconnected the "run" connector from the ballast
which is why it only fired in "start". With the "run" connector plugged
in is when I get no spark in start or run, but yes it does discharge
when I turn the switch back 1 detent from run...."accessory".

...I also just put a jumper wire across the ballast. With 0 ohms
I get 10.8v "run" and 11.2v in "start" on the coil +.

You put a jumper across the ballast in effect eliminating it correct? and you get 10.8V & is that w key on/not running (you said "run") or is it key on/eng running? Check w it running at a fast idle the voltages (1) across the batt posts (batt charging/running voltage) and (2)at the coil positive and at (3)&(4) both ends of the ballast w the neg meter neg ground probe touching the ECU case for these checks and touching the batt neg post for these checks. post what you get

Tonight I filled my primary fuel bowl through the vent. (No accel squirt, sitting since September or so)
by passed the ballast resistor with a jumper, and the engine fired quicker than my girlfriend's Chevy Cobalt,
Which i'm convinced hits the first cylinder every time.

A couple 1.0 ohm'ers on order. I still want to review my voltage numbers,
but theres no sense until the resistor is replaced. I'm feeling good about getting this one behind me.
No more hard start, low rpm hesitation, rich exhaust.

There are exactly two items that determine the voltage at the coil in run, the coil resistance and the ballast resistance. If the voltage to the ballast is in spec that is. Either your coil is internally shorted lessening it's resistance or the ballast is out of spec. Seeing as to how having your ballast plugged in also lowers your start voltage I am thinking is has a path to ground, probably not a clean one though. Out of curiosity, if you remove the ballast from the fire wall (keep it isolated from ground), but leave it plugged in to the wiring harness do your voltages go up?