Switched 12v source

You have to understand what I posted. What do you have for an ignition system, that is, does the system you have USE A BALLAST resistor?

This is important, because you can NOT simply hook the two together with such a system.

If your ignition uses a ballast, you are going to have to use the relay/ diodes mentioned,

............If not......they can be bridged.

You don't have to dig clear back to the switch, you can get at them in the engine bay. Go download a service manual for your vehicle or as close as you can get from MyMopar

What year/ model do you have?

Also if you have a "mostly factory" wiring harness, the BULKHEAD CONNECTOR has it's own set of problems, and when adding such a system as this EFI you really SHOULD use a relay to power the ignition loads under the hood.

So first here's what we need to know?

1....What year model is your vehicle
2....What are you gonna use for an igntiion system?
3....Is the harness factory stock, or been aftermarket re-wired?
4....Also, detail "what else" you are gonna add.......electric fans? "Big" electric fuel pump? Electric water pump? Etc?