Nice to see you are still making progress!
I finally got my act together and built you the small wiring piece you wanted. Here is a picture of the electrical “OR” circuit. I’ll put it in the mail to you on Monday.
For those of you wondering what the heck it is and why it is needed:
It didn’t/doesn’t take much electrically to start and run our cars. To START the car, you need power to the coil as well as power to the starter. Once it is running, you need power to the coil. That’s it – pretty basic.
Note: Wiring colors described below are for my 1970 Plymouth Road Runner. I do not know how much other cars and other years changed.
On a stock car, the key “START” position powers a brown wire that connects to the firewall. It connects to the “Q” position as shown in the FSM. From the engine compartment of the car, this is the middle connector, bottom row, second from the right. This brown wire continues in the engine compartment and connects to the coil side of the ballast resistor. So basically, when the key is in the START position, the coil gets full 12Volt power through the brown wire. Note that there is also a Yellow wire that connects to position “T” as shown in the FSM. As viewed from the engine compartment, this is the bottom connector, top row, second from right (just below “Q”). This wire continues to the starter relay and ultimately triggers the starter.
Once you let go of the key and it returns to the “RUN” position, a Dark Blue wire is powered. This dark blue wire powers a number of things that normally have power in the run position. From a coil perspective, it connects to the firewall at position N as shown on the FSM. As viewed from the engine compartment of the car, this is the middle connector, bottom row, left-most connector. This dark blue wire continues in the engine compartment and connects to the ballast resistor upstream of the coil. So in the RUN mode, the coil gets powered by voltage as reduced by the ballast resistor.
So with the stock setup is in the START mode, the brown wire is hot and the Dark Blue wire is not. In the RUN mode, the dark blue wire is hot and the brown wire is not.
The problem you run into is if you add something like fuel injection. This system needs power in BOTH the start and run modes, since it must be active to start and run the car.
But there is no wire in the stock setup that is powered in both the START and RUN positions. That is where the electrical “OR” circuit comes into play.
The electrical OR circuit contains diodes so it does not back feed other systems. One side of the “Y” (either red connector) should be connected to the brown start wire, and the other red connetor should be connected to the Dark Blue run wire (or other suitable wire that is hot during the RUN mode). The single blue connector is then powered in both the START and RUN modes - this should be used to power a switched lead that tells the fuel injection to turn on. Note that you may also need to power other coil related systems with it too. In my case, I also had to power my MSD box to provide power to my coil. The important thing is this electrical OR circuit is not meant for high power applications – it is meant to power relatively low power switched signals. The benefit to using this over relays is that there are no moving parts, and it takes up almost no space. It will use about a half volt of power, but that has not been a problem for me.
In my case, my brown wire was not used, since my MSD system powers my coil as needed – I don’t have a ballast resistor any more either. I simply slipped the brown wire out of the bulkhead connector at the firewall and used that end to power one side of my electrical OR circuit. For the run position, here are lots of powered wires to choose from. Note that in some cases you can connect to an unused connector like the headlights on buzzer if you don’t have that option enabled. This avoids any non-stock splices in your under dash wiring system.
Good luck with the install – let me know if you have any questions!
Hawk
