Hi,

I'm going to fit a master battery switch to my 144 (because I do a bit of light rallying) and I've seen 2 sorts:

1. a basic big switch (call it SW1) that just switches the main battery current. These usually have a big, red, removable key.

2. the same sort of switch, but with 2 or 4 little contacts in the base for switching the alternator output as well (call it SW2).

Now I understand that just using SW1 to switch the main current will not kill the engine as well, because the alternator just keeps on feeding the grid, but
will this work?
Run a battery cable direct from the battery to the + on SW1. Run the alternator to this + as well. Now run from the - SW1 to the starter motor. Also run ALL power circuits from the - on SW1 as well.
If SW1 is turned off, the engine should die as well as all the rest of the electrical circuits being isolated, because the alternator current cannot power any of the grid any more.

I'm sure I must be wrong, because otherwise they wouldn't have bothered inventing SW2, but I can't understand why. Help please.

Regards

JohnH