On your unrelated question - if you in fact are using a splitter you can expect to have problems. If you are using a MULTISWITCH, then the two lines are interchangeable. It does not matter which goes where, except...
If you are using splitters to feed the inputs to two multiswitches (which can be done), then you have to connect both multiswitches the same (as far as 13 and 18 volt).
Carl
If you are using splitters to feed the inputs to two multiswitches (which can be done), then you have to connect both multiswitches the same (as far as 13 and 18 volt).
Carl