Battery Isolator installation

Hello! I am working on a project and I've had a few issues with the Cartek XR battery isolator that I am using. I am helping fix issues in a motorsports level racing wiring harness as well as swap over to a Haltech PD16 PDM unit from a ECU Master PDM. The car also has a Haltech Nexus R5. Below is a description of the current problem.

I've installed the Cartek battery isolator as stated in the included instructions. The system comes with an included kill switch button that is wired to the Cartek unit and the haltech PD16. The 12v line going into the isolator is run through pin 26 on the PD16 which is a 12v line. The ignition line from the battery isolator goes to pin 13 on the PD16 which is the ignition pin. When supplied with 12v, this is what tells the PDM to turn on. Once the PD16 is on, it turns on the Nexus R5. I have two issues. Issue 1 is that I am unable to turn on the pd16 in this way unless I attach a 12v wire running directly from the battery to the wire coming out of pin 26 of the PD16 (even though this pin already is connected to the battery and outputs 12v which I have tested and verified). I can turn on the electronics of the car using a wire from the battery to power pin 26, which powers the cartek kill switch, making the system work like intended. The second issue arises when I try to start the car or turn on the fuel pumps. The starter is wired via a relay and the fuel pumps are wired through the system (all of this is controlled by a haltech keypad). If I activate any of them, the system shorts, and the PDM and ECU reboot. If I bypass the cartek battery isolator, running the ground directly to the battery negative terminal or chassis ground, the issues disappear. I can wire a switch to turn on the electronics and bypass the cartek and then the fuel pumps can turn on and the starter works. All the electronics on the car work and it can be put on the dyno.

Since I am redoing a wiring harness, I am assuming this is a grounding error in the system; however, I am confused as to why everything works when I bypass the cartek system. If anyone has any ideas for how I can troubleshoot the system, it would be much appreciated. Please let me know if there is any other information I can provide. Thank you all!

Doesn't the Cartek XR just switch the ignition to ground to turn off the ignition? I don't think it drives it high. So you might need to provide a pull-up resistor to get a high signal that isn't just a floating value from the PDM.

Thanks for the response David. From my understanding, the Cartek system just disconnects the battery negative from the rest of the ground loop on the car. I've tested this by checking if the chassis, engine block, and the multiple grounding points in the harness are in fact ground when the Cartek is on and off. When on, everything shows ground. When the cartek is turned off, everything including the chassis gets disconnected from ground.