I'm not sure about Silver Star, but Exiss and 4 Star have similar wiring as do most other brands.

Most 7 wire plugs do not utilise the center pin which is often used for back up lights. If you look at the plug, you will find six terminals around the outside edge. At the 1 oclock position, a red wire is used for the aux B+ feed. At the 3 oclock position the green wire is used for the right turn and stop lights. At the 5 oclock position, the black wire is terminated for the electric brakes. The 7 oclock position is for the white ground wire. The 9 oclock position holds the yellow wire for the left turn and brake lights. The 11 ocllock position is used for the brown wire which is your running lights.

Since you don't have a white wire, but instead a purple, I would suspect that it is the ground wire at the 7 oclock position. 

There are 2 different 6 way to 7 way adapters available.  Some are reversible. Some 6 way plugs have the center pin as the hot wire and some have the center pin as the brake wire.  Both ways are acceptable, hence the 2 different adapters.  I used to own one of each, but lately, most on the market are changable.  Simply take the screws out of the adapter and there will be only 2 wires that can be moved.  Simply reverse those two wire positions and your brakes will work like they should.

http://www.etrailer.com/Wiring/Hopkins/47549.html