Wiring question

[Kris 90]

I have a few wiring questions. I’ve installed a MSD box on my car and have a magnetic pickup distributor. I need an ignition wire to hook it to. I’m think it would be the red/green stripe wire that was originally on the coil +. Is that correct? My second questions is that on the MSD it has a white wire that can be used for a kill switch. Per the directions you run it to a toggle switch or button and then to ground. When you turn on the switch and ground it the car it will crank but won’t start. Do I need to use a specific amperage switch/ button for this? Ok my last question is what is the best wire to use for an electric choke? I’m also using a one wire alternator so Im not using the voltage regulator if any of those wires would do. 

[danno 128]

Unfortunately, the + wire  from the key switch to the + terminal on the coil is a resistance wire on the factory harness.  So you will not get the full 12 volts needed to run the MSD module.  There is no good place to get the 12 volts when the key is in the "run" and "start" position.  

Which MSD box have you got?   Some can work with a lower voltage because they have an internal relay system.

For the kill switch,  a switch rated for about 5 amps should work fine.  Keep in mind that this switch should never see any  amps going through it.  It is off when you want to use the car.  When it is on, you will not be trying to start the car.  The only time the switch will see any current is when someone is trying to start the car without knowing about the switch.   You also might be able to ask MSD the amperage needed for the switch, but I would think 5 amps is fine, 10 amps is plenty. 

 

[1969_Mach1 333]

I use the 12V switched source for my MSD box directly at the ignition switch. Yes there is a terminal at the ignition switch that has 12V in both run and start positions.  For Mustangs that did not come with a factory tach, this is the same terminal the the original resistor wire is attached to.

[Kris 90]

I have the 6al box. The directions for my box show to hook it up that way but wanted to make sure before I cut the 90* end off my new gauge feed harness. 

[danno 128]

OK, this is what I am thinking.  I think the red wire to the ignition turns on a relay in the MSD box. There is very low  current in the red wire, it is only turning on a relay.  Try it with hooking up the red wire to your msd box to the resistance wire that used to go to your coil.  I will bet it will work fine. You can measure the voltage where the red wire connects up to the existing resistance wire in your harness.   I will bet it is over 12 volts when the motor is running, which is fine. 

If you have doubt, ask msd if you can hook the red wire up to the resistance wire that used to go between the ignition switch and coil. 

[Kris 90]

That’s what I was thinking was it was just using it for a signal to turn on the MSD. I wasn’t sure if moving that wire off the coil would affect anything on the gauges since it’s in the gauge feed harness.