Confused on wiring Distributor and Coil

[jojothemonkey]

I have Megasquirt II PCB 3, with the direct coil drive installed. I am also using a relay board.

 

Distributor with the three wires

Black is ground - goes to frame or engine

White is trigger - goes to Tach on the relay board

Red is 12v - goes to ???

 

Coil

Negative terminal - S5 on relay board

Positive - Depends on what relay board diagram I have looked at ties in with the fuel pump power supply or ignition switch

 

Now if I look at this diagram

Terminal #5 shows the positive side of the coil being connected to the fuel pump. Why not my ignition switch?

Terminal 15 shows the white wire on the distributor being tied in with a switch 12v. WHY? As stated above the red wire on the distributor is 12v then why does the Tach wire require 12v also? The way I see the distributor wires is ground, power, and signal.

 

Then if I look at this diagram

It shows the O2 sensor is tied into the fuel pump.

The positive side of the coil goes directly to a switched 12v source.

 

This post may not make a lot of sense. But I am confused as heck as to why things are wired like they are.

 

 

One more thing, what size fuses should be used for the fuel injectors, 5amp or 7.5amp?

[Careless]

My guess is that the 02 sensor is heated by the activation of the fuel pump relay. The wire going into the relay board is the actual voltage/resistance wire used for the reading. The one running to the fuel pump looks to be the heating wire.

 

and the + Coil post is connected to the switched 12 for the the same reason. It loosk to be using the S5 from the relay board to trigger a fire, since you couldn't time the firing without running an additional 12volt line through the relay board if you were to have it hooked up to the + instead, and then have the coil grounded to chassis. This makes it easier by using the ground connection to trigger the closed circuit.

 

That's what I THINK. don't quote me on that

[jojothemonkey]

That makes sense to have the coil positive and negative all in the same circuit. But I still do not understand why there should be two separate sources of 12v going to the distributor. I see that by connecting the resistor it should drop the voltage down to around 5v. But where is the main 12v wire suppose to connect to. This is an 83 distributor. This is frustrating as this is pretty much the last thing to figure out before I can attempt to start the car and before I move to Houston next week and have no where to work on the car.