Fuse 3 and aux battery relay wiring mods due to house battery

[kevinm]

Hello,

Electrical novice here, toying on a 90 westy with a pretty much untouched electrical system. I'm planning to add an aux lithium battery and want to power the fuse 3 items from it: interior lights, stereo (basic setup; no amps or subwooofers) and lighter. From what I have read, you can either 1) run a fused wire directly to the non-hot fuse 3 tab in the fuse panel (probably the top tab for my year but check first) , or 2) cut the feeds from B11 and B12 on the red multi-point harness and connect a fused wire to both these wires. Is that right? It looks as if either would work, and I like the idea of not cutting anytying, as I get the heebie jeebies about doing things that can't be easily undone. But for others who've thought about this or done it, do you have any recommendations on one over the other?

Follow-up: once I've done this, will the sink pump, along with the fancy battery level and water level indicators be powered from the new fused 3 wire, or instead do I need to connect the wire from terminal 87 of the existing battery cutoff relay in the driver side battery box to a new fused wire from the aux battery? If I do this can I bypass the 8-amp fuse on the driver side b-pillar (since it will be fused upstream anyway)?

Sorry for all these questions. I've been trying to find clear answers but it's still a little muddy. Thanks.

- Kevin

[ProspectiveOwnergon]

This is what I'll be doing once my van comes back from rust repair.