'68 igniton switch and MSD/Holley EFI ignition box wiring

[rmchrgr]

I posted this on Moparts but did not get much response, hoping I can get some more input on what what I am doing here to try and confirm if will work and be safe. I changed some things from my post over there to try to make it clear. See pics below.

Generally speaking, aftermarket ignition systems like MSD want to see the full 12 volts while cranking and in run. The OE switch functions do not allow that to happen because of the OE ballast resistor bypass function so when you start the car, there is a moment when there is no voltage coming through the IGN 1 circuit.

So what I am doing is "tying IGN 1 & IGN 2 together" right behind the switch and then tapping the red ignition box signal wire into that circuit. In this application the ignition box drives the coil and there is no ballast resistor so those output wires have been eliminated.

I am working with an aftermarket wiring harness so imagine the pink wire is the OE blue for IGN 1. The small red wire spliced to the looped brown IGN 2 wire is for the ignition box signal.

I left the molded plastic switch connector off to show how the wires connect to the switch terminals.

My concern with this setup is that the IGN 2 terminal on the back of the switch is always going to be hot even when the key is released to the run position. I believe this is what aftermarket ignitions generally want but I am not sure if wiring it directly behind the switch this way will overheat the contacts inside the switch.

If that's a distinct possibility, can anyone recommend a different/better place to make the connection between IGN 1 & IGN 2?

I have seen where a relay can be used to handle this situation but I'm not sure how to wire it properly without the ballast or coil outputs.

Thanks for any input.

Greg

 

[6-david-5]

I addressed this recently with my '68 Dart! I installed a newer-model MSD 6AL in the car & realized the car wouldn't start because of this very issue, just as you describe it. My solution: Eliminate the ballast resistor, & break out that white jumper wire that comes with the MSD kit! Link both of the ballast resistor push-in lugs together with it, and connect the 12V turn-on circuit for the MSD at that point. I've been running the car that way since & have had no trouble, and don't expect any.

Remember, you are just providing low-amp turn-on signal using this circuit--which should be similar to the low-side of a 12V relay. The bulk of the amp draw for the MSD happens through the thick-gauge power wire (14 or 12 gauge, I believe) thats supposed to be going to the battery. I don't feel it would be any trouble to "turn the MSD on" continuously as you are doing it--remember, that circuit is no longer powering the coil with the ballast resistor inline.

Happy Easter.

David

 

[6-david-5]

My concern with this setup is that the IGN 2 terminal on the back of the switch is always going to be hot even when the key is released to the run position. I believe this is what aftermarket ignitions generally want but I am not sure if wiring it directly behind the switch this way will overheat the contacts inside the switch.


Greg

Greg

You really had me thinking about this one, but I don't believe this is of any concern. IGN 2 is momentary during the crank-position, which means that although there is potential on that wire, it is disconnected throughout the time the car is on and running. It is only there to supply a full 12 volts to the coil during cranking, therefore, there should not be any "build-up of heat" because the circuit goes OPEN right after you start the car.

You can verify this easily with your switch out on the bench as you seem to have it--if you have a meter, do a continuity check between BAT & IGN 2. I would expect to see no continuity until you turn the switch to crank, and see it go open again when you release the key!

Anyone is welcomed to correct me here if I have this wrong, but when I look at a wiring diagram, that seems to me like the most likely explanation.

Happy easter everyone.

David

 

[rmchrgr]

Thanks for the reply David. I did eventually get an answer on the other site which confirmed my method as sound. But just to elaborate, yes the load the red wire puts on the circuit is minimal so it will be OK to run it like I have shown.

Though it was a little tricky to do, I did the test like you described with the test leads on BAT and IGN 2 and the results were as expected - no continuity until the switch is turned all the way right and when released the circuit is opened again.

However, my original concern was that since I now have IGN 2 permanently jumpered to IGN 1, there will be current going through that contact on the switch continuously while in run where it hadn't before.

Though they don't tell you exactly how or where to join the circuits, this is what MSD/Holley etc. instructs you to do when wiring one of their ignition boxes so it has to be done one way or another if it's going to work properly. Besides, there's enough of our cars out there with MSD ignitions wired like this in some manner and I've ever heard of anyone's dash board melting because of an overheated ignition switch. Not sure that making the connection somewhere else downstream would be any different.

 

[HEMI-ITIS]

First you need to install a new carpet...........LOL The more voltage going to the MSD the more the MSD will put out.I have the ignition on a toggle switch which in turn makes hot starts and engines with high compression ratios easier to start. Use the key or starter switch to spin the engine and flip on the ignition switch. I have my 6al-2 programmable set up that way.Toggles for fuel pump,fans and ignition.

 

[6-david-5]

However, my original concern was that since I now have IGN 2 permanently jumpered to IGN 1, there will be current going through that contact on the switch continuously while in run where it hadn't before.

Though they don't tell you exactly how or where to join the circuits, this is what MSD/Holley etc. instructs you to do when wiring one of their ignition boxes so it has to be done one way or another if it's going to work properly. Besides, there's enough of our cars out there with MSD ignitions wired like this in some manner and I've ever heard of anyone's dash board melting because of an overheated ignition switch. Not sure that making the connection somewhere else downstream would be any different.

Greg

Thanks for reporting back on the continuity test--you've confirmed what I thought was true!

And you've also confirmed that your wiring change will be of NO CONSEQUENCE. Making this connection downstream--like those of us that join both leads from the ballast resistor together--is no different! I think we're really just talking at this point, but you have shown that IGN 2 contacts will be open during vehicle operation, and will pass NO CURRENT. Therefore, there is no heat to build up in the ignition switch assembly.

Remember, that brown line (IGN 2) has ALWAYS had potential voltage coming from "after" the ballast resistor (less than 12V). IGN2 being open during RUN makes this inconsequential, and has always during the car's life! We all know that as you proceed with your wiring mod that you're going to be fine.

I used to wire MSD's from the blue ignition power wire, which was after the ballast, so I used to turn them on with the "reduced" voltage. They always worked & stayed on--just with a little less voltage. The heavy-gauge wiring always assured it performed as expected.

David

 

[rmchrgr]

First you need to install a new carpet...........LOL
The more voltage going to the MSD the more the MSD will put out.I have the ignition on a toggle switch which in turn makes hot starts and engines with high compression ratios easier to start. Use the key or starter switch to spin the engine and flip on the ignition switch. I have my 6al-2 programmable set up that way.Toggles for fuel pump,fans and ignition.

The red wire in question is the trigger wire which only turns the signal on in the box, there's only a small amount of current running through it. But either way it will get full juice because it's now permanently tied to the "run" circuit. Don't need the crazy race-car ignition switch with the bone-stock 383. Maybe when the 470" goes in...

Plus, I can't finish the carpet until I finish the wiring. Baby steps, Al, baby steps.

 

[rmchrgr]

Greg

Thanks for reporting back on the continuity test--you've confirmed what I thought was true!

And you've also confirmed that your wiring change will be of NO CONSEQUENCE. Making this connection downstream--like those of us that join both leads from the ballast resistor together--is no different! I think we're really just talking at this point, but you have shown that IGN 2 contacts will be open during vehicle operation, and will pass NO CURRENT. Therefore, there is no heat to build up in the ignition switch assembly.

Remember, that brown line (IGN 2) has ALWAYS had potential voltage coming from "after" the ballast resistor (less than 12V). IGN2 being open during RUN makes this inconsequential, and has always during the car's life! We all know that as you proceed with your wiring mod that you're going to be fine.

I used to wire MSD's from the blue ignition power wire, which was after the ballast, so I used to turn them on with the "reduced" voltage. They always worked & stayed on--just with a little less voltage. The heavy-gauge wiring always assured it performed as expected.

David

I've never taken an ignition switch apart but I don't think I have to now because I finally understand how the thing actually works. Before my reverse-engineering epiphany here, my thought was that the constant voltage from the run wire would back feed through the jumper wire to the IGN 2 contact causing it to get hot.

But thinking about the physical operation of the switch made me realize the IGN 2 connection is mechanically-actuated. Turning the key to crank rotates the contact points inside. This closes the circuit allowing current to flow through it to do it's job of cranking the car over. The rotation part is the "key" here, because while that is happening, the run circuit is opened (no current flow).

Once the car fires, you physically release the key and the spring returns it to the run position. As the spring releases, the contacts inside are rotated back, closing the run circuit. This opens the crank circuit and stops current flow through it.

Basically he jumper wire creates a bridge to eliminate the loss of current when the key is turned all the way right to crank. And since the red wire is now attached to the run circuit through the jumper, it will get the voltage from the run wire. However, voltage going through the jumper wire after cranking won't do anything to the ignition switch itself because there is no longer a physical connection for the current to flow through when you let go of the key.

I mean duh, of course that's way it works, it's practically ancient technology. It's only taken me oh, 25 or so years of messing with these cars to finally grasp that but hey, better late than never.

Thanks!