Tripac APU "Pre Evolution"

[Lonestar10]

My APU had the alternator die last week so got my new alternator and installed now it wont start.

come to find out the fuel shutoff solenoid is not receiving an open signal. as i can take the shutoff solenoid out and the apu starts right up and runs.

What is all required for the shutoff solenoid to get open voltage?

so far i have checked
wires on alternator - 50amp Maxi-Fuse is good.
where apu shutoff switch used to be is bypassed so not a bad shutoff switch.
I have 1 Volt on RPM sensor above flywheel not running.
all fuses on computer board are good and the 3 or 4 on wires we all good.
i have also hooked up the shutoff solenoid to 12vs and it actuates fine.

Im unsure how to check if RPM sensor when running what to look for.

what else tells the fuel shutoff valve to open.

any help would be greatly appreciated.