And ALL the electrons that flow out of the negative side have to flow back into the positive side. Resistance anywhere in the circuit causes a voltage drop and reduced power delivery to the load.

The whole system needs to be the very best it can be on every connection with the proper size conductors

I scope engines all the time and when I want to check injector sequencing I sync the first trace to an injector and then want to see the plug firing sequence. Sure ignition is noisy, but all I do is wrap a short 4" piece of insulated wire around the plug wire (Definitely don't connect to the wire itself). Essentially I make a small coil around the plug wire. The result is much easier to see even though you see the other seven as well. Takes 5 minutes and no high voltage probe needed.

BTW Mark,
I have the same Tek scope as you but when I'm on the road going to a tune job I carry a small USB scope from Pico. I bought the 2205A for about $200, which is 25MHZ, two trace, uses the laptop for the display, and is so small it fits in my laptop case. You might want to check it out.

Dickie the mad scientist

Thanks Rich, good idea on the inductive pickup...I would not have thought of that idea😀