MSD 6A battery kill switch wiring

This is probably one of those situations where I go "DUH!!" when I figure it out, but here's the question:

Wanting to be NHRA legal, I have a 1/0 battery cable from the rear battery through a kill switch to the starter, then to the big post on the starter relay. I have the alternator charge wire to an aftermarket control/fuse panel under the dash, then to the hot post of the starter solenoid. (The field wires to the voltage regulator.) Ignition is fired by an MSD 6A box. MSD says I can ground either the white or violet wire (whichever is NOT used to power the distributor) to kill the ignition.

I have a 4-pole heavy duty QuickCar battery kill switch next to the rear battery battery. I can kill the battery positive, of course, and I'd like to use the small poles to ground the ignition... but how do I do this?? The small switch poles are closed (connected) when the battery is in the system, but open when the battery is disconnected. Opposite of what I want. So is there a simple way to ground the MSD box with this switch? I can't run to ground through the switch or the ignition is grounded when the battery connected. Am I missing something obvious?

I know there are other ways, but don't to complicate things. If I can ground the ignition and ALL battery power to the front is disconnected, I'd be good.

I would not ground it, I would break the power. In fact a 4 post switch, unless it's set up for a magneto, is a open when off switch. Just wire the small contacts in series with switched (ignition switch) "run" power and use the output to feed the "small red" on your MSD, and for good measure your fuel pump relay if you use one.

67Dart273 said:

I would not ground it, I would break the power. In fact a 4 post switch, unless it's set up for a magneto, is a open when off switch. Just wire the small contacts in series with switched (ignition switch) "run" power and use the output to feed the "small red" on your MSD, and for good measure your fuel pump relay if you use one.

Click to expand...

Thanks! And yes on the fuel pump relay, so thanks for that tip.

67Dart273 said:

I would not ground it, I would break the power. In fact a 4 post switch, unless it's set up for a magneto, is a open when off switch. Just wire the small contacts in series with switched (ignition switch) "run" power and use the output to feed the "small red" on your MSD, and for good measure your fuel pump relay if you use one.

Click to expand...

This is how Ive wired mine...two stages of protection I figure

So I understand that in my case I could break the circuit either between my ignition switch and the fuse panel, or between the panel and the MSD box, then run that through the rear switch small posts, then feed the fuel pump relay from after the rear battery switch.
Correct?

Your wording is confusing.........

What is the "last thing" before the power gets to the MSD "small red?
Same question the fuel pump relay.

I don't know how you have things wired........original Mopar ignition switch is not fused.

But essentially You have battery.........maybe a fuse, maybe not.........ignition switch.......back to disconnect.........back up front.........to MSD and to pump relay

67Dart273 said:

Your wording is confusing.........

What is the "last thing" before the power gets to the MSD "small red?
Same question the fuel pump relay.

I don't know how you have things wired........original Mopar ignition switch is not fused.

But essentially You have battery.........maybe a fuse, maybe not.........ignition switch.......back to disconnect.........back up front.........to MSD and to pump relay

Click to expand...

Got it! Perfect, will get it done tomorrow. Sorry for the confusion!!

If running the blue/brown wires looped together to turn on your MSD, run those wires back to the cutoff small stud and a wire forward back the the MSD. Throw cutoff, the energy to the MSD switched wires goes dead, car turns off.

Run the fuel pump relay trigger off the same side as the wire heading back to MSD, kills that too...

Not my favorite way to do things, but works.

Success. Ran ignition feed for MSD back through the 4 pole switch, then to MSD small red wire. I did also power the fuel pump relay off the same wire as MSD, now when I turn the rear battery disconnect, the 340 definitely stops running!!

Thanks for the help!