I ordered the VisiStop front and brake light modulators,  they sell them as a set on the site...

http://www.comagination.com/bflasher.htm#COMBO

I got the front one in no problem and it works great.  My issue is with the rear.  

The instructions say to splice the black and red wires of the modulator to the Black wire to the brake light (+12 vdc supplied from brake switch activation).  

The green wire of the modulator goes 'to battery negative (-) usually ground in U.S.'

They don't want me to hook the wire up directly to the battery do they?  

Can't I just attach that wire to any metal part of the bike to ground?  

To make matters worse, when I took off the seat to get to the wires I have a brown wire, a mostly black wire with white stripe and a mostly white wire with a black stripe.

I am completely at a loss.  Can anyone help with this?  

Here is a pic of the wires on the bike.  Before I start cutting wires I would really like to know exactly what I'm doing.  An electrician I'm not but I can do this easy if I know what is what.

As always, your help is greatly appreciated.

Thanks for the info.  I will be installing today after work and I will post my results for all interested parties.