Electric fuel pump wiring
FYI you do know that you do compression test without the ignition and fuel being on anyway on all cars. And your fuel bowls will still fill up with your ignition being on or off the carburetor bowls that are empty of fuel they don't care whether they ignition is or not. And if you want to prime your oil pump weill leave the ignition and fuel pump off and just turn the motor over until the oil pump is primed.
I actually have my son crank the motor with the ignition key when doing a compression test, you could always jump the starter relay under the hood but I’d rather not.
The ignition doesn’t trigger on my car when I do a compression test using the key as I can either hit the ignition kill switch (NHRA requirement for having my battery in the trunk) or I can pull the fuse out of my digital ignition box when I perform a compression test.
You are correct that the fuel bowls will still fill with the pump wired with the ignition but the pump would also be running if I had the radio on and the motor off which I do not want to happen.
I also look at this as a theft prevention system as a potential thief wouldn’t be able to drive very far without having the electric fuel pump on, my switch is mounted in the map light location so odds are pretty slim that they would turn it on.
Never had an issue priming my oil pump but I can tell you that California’s wonderful new gas blend will evaporate really quick from your fuel bowls so it’s nice to hit the fuel pump and prime the bowls before firing the motor as modern pump gas is formulated to be under pressure (fuel injection, not sitting in vented fuel bowls).
Like I said, either way will work, this is just my preferred method.
