Started working on the cut off switch today, here is my final schematic
When the key is taken out, the line is cut off.
The spare battery connection is temporary, to use this spare, take the key off for the main battery.
When the spare is not use, take the key off for the spare battery, this will make sure the wires to connect the spare battery is not hot.
Take both keys off when TT is parked or when charging the main battery with a solar panel; the spare battery could be on while charging the main battery.
I finished installing the first cut off switch but had to stop because the first test failed. I use a multimeter to find the fault and found the switch to be defective. There goes an hour wasted. I learned my lesson...always check the parts for defects before using it.
The wiring connections to the battery is completed.
A battery tender with a fuse is installed for connecting the solar panel directly.
Cut off switch part
The test failed, no current going through when key is on.
I have to get a replacement part and should be able to complete this project tomorrow.