Question on splitting power/signal PDM and EMU

I’m currently learning how to design wire harnesses while simultaneously programming the PDM and ECU, which is proving to be quite a challenge. I’m working with the PDU16 and EMU PRO 8 on a prototype racecar. I’ve just completed a PDM installation course and am now progressing through a motorsports harness course.

Here’s my first question: For the ignition coils, if the PDM is controlling the power, is it standard practice to route the coil signals to the PDM and allow the ECU to manage control via CAN? Alternatively, can the EMU PRO 8 handle both the power and signal responsibilities, leaving the PDM to manage only high-current circuits? Or is it better to route coil power to the PDM and coil signals directly to the ECU, even though this complicates harness construction?

Possible race car logic:

- Master Switch turns on ECU.

- ECU sends messages to PDU for things it is setup to control (ie, Fuel Pump, Cooling Fans)

- Ignition Switch (could be connected to ECU (which informs PDU), or to PDU with keypad) controls power to things that need to be on for engine to run (Ignition Coil Power, Injector Power).

- If the PDU activates the starter relay, then turn off things like lights, electric water pump, cool suit pumps while the starter is running to provide maximum current to the starter.

-- If PDU is powered (ie, alternator is providing power) and can detect Master Switch is off (ie, kill signal) -- it should disable the ignition power, so the engine will stop.

To answer your questions The coil signal control needs to be wired directly to the ECU. The power to the coils should come from the PDM, but you can choose if it's the same power as the ECU or separate. If separate, the ECU must always be powered when the ignition power is active, otherwise you can back-feed power into the ECU.

David, thanks for that. I’ll look through my notes and compare to your suggestions.

Since you're doing paddle shift in the ECU, the ECU would send a messages to the PDU to turn on the gear shift pressure pump. That is an example of something that could be turned off while cranking the engine.

By keeping ignition and ECU separate, you can crank the engine to build oil pressure before turning on the ignition to allow the engine to run.

I think there are a few ways to achieve what I'm trying to accomplish but I'm struggling to figure out the best way to run the large current draw power and ground leads within the harness so that the signal and reference wires end up at the ECU and the large power draw devices end up at the PDM while having a clean appearance.

On top of that i'm not confident in the choice of connectors to use for this. I have a box of good used Autosport connectors that I want to use on this project and my goal is to have a very modular harness with junction boxes that have small AS connectors to each sensor.

Couple of concerns are:

Water pump needs large power lead but will also be PWM controlled. I could just run this to the PMU16 and and then let the PMU send information to the ECU via CAN but I think it's better to run all the analog/digital/pwm connections to the ECU. What is a good way to construct this using AS connectors that have low current pins? I can use multiple pins to spread the current but I could also just separate the power wire and try to group all of the power wires from devices in the in the engine bay and have that be a separate harness but I'm struggling to find a clean way to do this.