Just installed HEI and having touble starting

[whateverpratt]

Background: I have a 1963 C10 with a 230 that I haven't tuned in 10+ years. It ran fine, but high rpms suffered. It always started easy; all you had to do was bump the key for a second (maybe 2 or 3 if it was cold). I figured it would be an upgrade if I put an HEU unit on the truck. I got a complete setup (distributor, cap, wires, and coil) for $30. I installed it last weekend. It started right up and ran like a champ.

Problem: fast forward to today, and I'm having touble starting my truck. It started up fine when I went to put gas in it. After filling it up, the truck wouldn't start. I had to get a jump from friendly passerby. I drive the truck home, shut it off, and try to start it, but it does the same thing again. I turns over, but it doesn't sound like it's firing at all. I hook it up to my wife's car, and it starts.

I'm pretty clueless when it comes to electrical, but just the same I pulled out my multimeter and started measuring volts at different spots. My battery was around 12.5 (not running). With the key in the on position, the wire going to my coil read 12.4 (this wire is hooked to a terminal on my ignition that shows 12+ volts when the key is in the on position); however, when I had my wife crank the engine, the wire to the coil measured anywhere from 8-10 volts. I also measured voltage at the battery while my wife attempted to start the truck, and it measured about 10.7 or so during cranking.

I am assuming that voltage drop at the coil is my problem, and that the other battery provides enough voltage to keep the volts up at the coil to start the truck. BUT, I have no idea because I really don't know what normal is, and electricity is black magic. What I do know is that before the swap the truck started super easy, and now after the swap the truck has started cold a few times but refuses to start when warmed up unless you jump it. I'm very curious to see if it starts tomorrow without any assistance.

How do I fix this?