[TR] TR3 Electrical question

[Carl TR]

This weekend I am working on installing the Wiring Harness on the '3
Project.

I have installed a Lucas Battery Master Switch (Model ST330) under the dash.
In addition to the battery / ground connections there is a connection for a
wire that is supposed to go to the coil.   
There were no instructions with the switch.  

In the harness there is a white wire that goes from coil (- side) to the
fuse box (A3).   

The question is: does the battery switch (coil) wire replace the one from
the harness?  But that doesn't make sense to me since the switch is coming
off the positive ground side of the battery.  
Or does it connect to the LT side (+).   I guess my confusion is I can't
figure out how the connection from the switch to the coil functions.  

Distributor  [WB] ->   + (LT) Coil -  [W]  ->  A3 Terminal on Fuse Box

Battery (+)  ->  Switch  ->  Ground (at Starter)

Switch image at
http://www.retroclassiccarparts.com/components/com_virtuemart/shop_image/pro
duct/Battery_Master_S_4c40bf3e0a745.jpg the coil wire comes off the brass
fitting visible in the image.

Thanks 
Carl
TS81802LO getting closer to being on the road...