Made some progress this weekend.
Took some pics but I haven't had time to post them yet, or the schematic (sorry
) You know the story: wife, mortgage, job.
Relocated the lithium battery to the trunk, was formerly on the floor behind driver's seat. Installed one fuse (one more is planned) and all three planned switches. Two of the switches still need to be mounted on a project box so they don't float around on the floor behind the driver's seat.
The switches as set up enable quickly switching between the lithium pack and the lead acid main battery so that either can support the car. You do have to stop the car to make these changes. This will be used most often to switch to lead acid power for the car while charging the lithium pack. Also with the lead acid pack in the circuit, the alternator can be switched on to support long night trips with headlights, which the Lithium pack can't handle. The lithium is good for at least three hours drive time without headlights.
Gotta edit that circuit schematic to show what I actually built, and post it... and the pics too.