Yes, I know it's been asked hundreds of times, but I'm going to ask again.
Also not trying to make this into a "HEI vs duraspark" debate.
HEI Batt terminal needs to see 12v at crank and run. As I understand it, there isn't an existing wire in the harness that has both.
The existing coil wire will only have 7-9v on run because of an inline resistor so that can't be used.
I've see some advocate using a 10g wire off the "I" solenoid terminal for the 12v on crank.
I've also seen other posts mentioning that I could use one of the wires going to the duraspark for the 12v on run.
I assume I could splice both of these together and plug it into my HEI?
Does It matter that I'm tapping into a smaller gauge wire if I'm splicing into the duraspark wire for my 12v on run wire?
Any problems w/ the "I" solenoid post seeing a constant 12v on run?

Bear with me...wiring is not my strong suit.
Thanks

 

update
after a bit of research, I think i'm going to use the power wires to the duraspark to run the HEI.
There are 2 wires that power the duraspark, one white/brown and one red. The white/brown one is 12v on run and the other is 12v on start.
Last night, I removed the starter cable from the solenoid to test those wires without cranking the engine.
I have 12.4v at the battery but no signal at the wires.
Not entirely sure if I'm fully understanding how to use the multimeter or if there truly is no power at these wires.
I have the multimeter on DC and can get a 12v reading on the battery itself. The Duraspark wires should be coming directly from the ignition switch.
I'm trying to ground my tool to a bolt on the inner fender, so maybe I have a bad ground.
I was thinking of using a voltage test light to see if it'll light up. Not sure what the problem is.
Also, my HEI is asking for 12v on crank and start. Assuming the duraspark wires are working as they should (car was starting fine before I pulled things out) I'm guessing I should be splicing the 2 wires together and attaching them to the BATT terminal on the HEI, right?

 

I'll have to look at my 77 F250 tonight, I went HEI on it and IIRC I used one of the terminals off the DS with a spade for it...

 

HEI should be wired to the trash can / Chevy vehicles. Kidding aside, it looks like you can use the DS modules +12V feed or original coil + to trigger new 12V relay.

 

OK, hopefully this helps someone else who is trying to do the same thing.
I figured out my multimeter issue. Bad ground.
I was trying to ground to the inner fender well. I assumed it would be fine to use but was wrong. When I grounded the tool directly to the block, I was able to see a full 12v on run.
I'd assume the inner fender could be grounded to...after all, the solenoid is grounded to the fender, right?
So for my HEI that requires 12v on start AND run, I'll be using both wires going to my old duraspark module and splice them together. I'll also use this for my electric choke as it runs in the same vicinity as the carb.

 

update.
do NOT use both duraspark white and red wires, as it'll send 12v back to the solenoid when in the run position and your starter will engage while in run.
I finally got a test light on the wires. The red wire is hot on run and start, the white one only on start.
I'm using the red wire to give 12v to my HEI as well as my electric choke.