12/12/18 boatmotor, lithium install diagram

Looking for a diagram to wire 12/12/18 isolated dc/dc charger. I have a mercury outboard motor with 18amp alternator, 1 LiTime lithium 140amph battery, 1 Dakota lithium 60amph battery and a 3 way switch to send charge to only 1 battery at a time. Does anyone have a wiring diagram? Should I add a fuse to this circuit? How many amp fuse?

I assume you still have the lead acid starter battery, this is necessary as the Orion does not work direct from an alternator. The wiring diagrams and recommended wire size and fuse sizes are all in the manual.

https://www.victronenergy.com/media/pg/Orion-Tr_Smart_DC-DC_Charger_-_Isolated/en/index-en.html

I am really confused. I thought I needed it to keep the lithium battery’s from charging too fast so the victron needed to be in between the motor in the batteries. I was planning on getting rid of my current age battery to reduce boat weight.

So your saying keep the age and connect the motor alternator direct to the age, then the victron then my lithium battery 3 way switch then the two lithium batteries, correct?

The boat motor which will be running 8 hours per day will charge all 3 batteries?

Sorry spell check changed AGM to age

Yes, look in the manual it shows the starter battery, it needs this to allow the alternator voltage control to work. When people have tried connecting the DC to DC direct to an alternator the voltage swings up and down.

Motor to AGM, AGM to Victron Orion, Victron Orion to switch, switch to the lithium batteries. This way will control and limit the lithium charging.