I would check the wiring between the two units, and the state of the remote unit.
The manual details the following on page-5:
Blinking DELAY 1 Indicator
In Maintained Mode, the DELAY 1 LED on the PS-8R blinks whenever the
unit is OFF (the remote switch is in the OFF position).
In Momentary Mode, the LED blinks if the “memorized” state is OFF.
Also stated on the same page:
Be sure that the mode (momentary or maintained) of all units is set
Momentary mode and Maintained mode are explained on page 4.
If you do have more problems, you may try calling their technical support
[EDIT based on comments]
This particular power sequencer needs a remote switch for power on or off. The wiring is described in the manual on previously mentioned page 3/4, and is dependent on the jumper setting on the main board. To change the jumper setting on the main board one need to open up the unit.
I would strongly advice you not to open the unit if you are not certain. It is impossible to asses your expertise in this, hence this warning. If you are not experienced in this, please contact an experienced installer and|or call Furman support.
The fact that you have disconnected the cables is probably going to further complex the situation if you do not recall the original wiring (which wire connected to what terminal), unless you have taken note when disconnecting. And some of the wires very likely go to the remote switch which you need to turn this unit on.
It is a mains unit, so whatever you do, disconnect before doing anything !
[EDIT based on logical thoughts]
As you have disconnected all cables, there is no connection at the terminals at the rear of the unit. Given the fact that the unit is blinking, without any wires, It could mean that the jumper is installed on JMP2 which is "Momentary Mode".
It is likely that this particular situation is "Memorized OFF" in "Momentary Mode", which means if you connect
REM terminal, just momentarily, with
+12V terminal, the unit should come on.
However I cannot be sure of this !!! ... at your own risk ...