If it is a "B" generation (LDC panel) the curtis BDI circuitry is different than units that are installed on trucks with contact hydraulics. Top cover of the Curtis will have Cat part number. Output from Curtis goes to a pin on the logic unit to allow hydraulics or if battery is dead, you will have extremely reduced hydraulics. I will have to dig out the sea scrolls to see if the logic input is High or Low at which situation.
On Curtis controller, terminal #2 (old large box) terminal #3 (later smaller box) if you read appox. 12 volts with respect to B- then the truck will be in lift lock out (reduced). With properly charged battery the voltage at terminal 2 or 3 should be zero. The wire that connects to the terminal should be PU/B (purple/black tracer) and inputs to the logic unit at card edge connector J2-R. Also check for voltage drop on the B+ wire to the curtis and on the B- wire to the curtis. Try disconnecting the PU/B wire from the curtis to see if hydraulics come back.