Unfortunately this is characteristic of Victron. And even more frustrating when there is no technical support, just “contact your dealer”. Do you really think Fisheries or Defender or Amazon would be able to answer the question?
Then instead of going for the lowest of the lowest price, you buy at Peter Kennedy. PKYS.com. always got good explanations,
and an Argo Fet is real basic....
if you look to the manual which is at victronenegry.com it shows on a nice drawing how to connect the ArgoFet
12/24 Volt auto ranging
The Argofet will automatically adjust to a 12V or 24V system.
Alternator energize input
Some alternators need DC voltage on the B+ output to start charging.
Obviously, DC will be present when the alternator is directly connected to
a battery. Inserting a Diode or FET splitter will however prevent any
return voltage/current from the batteries to the B+, and the alternator will
not start.
The new Argofet isolators have a special current limited energize input
that will power the B+ when the engine run/stop switch is closed.
Installation (see figure below)
1. Always disconnect the battery minus cables before making
alterations to the electrical system.
2. Connect the positive output of the supplying source (alternator) to
the input of the battery isolator.
3. Connect the positive connection of the battery sets to output 1, 2 and
(optional) 3 respectively.
4. Connect the ‘Energize’ blade terminal to the engine run/stop switch
(optional). Minimum cable cross section: 2,5 mm².
5. Connect the ‘Ground’ blade terminal to the common negative bus
bar. Minimum cable cross section: 2,5 mm².
6. Connect the negative poles of the battery sets to the common
negative bus bar.
The blue LED will light up when voltage is present on the input of the
Argofet.