It is on the bottom of the pump on the port closest to the engine.
Mainly troubleshooting at this point since I pulled the manual pump and put electric priming pumps on it.
The 818 design has it dump the prime into the intake and I'm a little hesitant about that so I was looking at a separate place to dump it.
Right now I have one pump acting as the prime dumping into the intake and another dumping into the return off the injectors but I think the pressure is too much on that line so I'm looking at other alternatives.
Since I'm designing a ecm module to control the truck I want to tie in priming function as an automatic function and since I now know the other port comes off the main pressure feed I can place a pressure sensor there to control the prime function and monitor the injector pressure.