2007 Toyota Rav4

I have a 2007 Toyota RAV4 with 3.5 liter engine with less than 1k miles. I plan on towing it behind my class A motorhome. For additional stopping power, I will install a Roadmaster BrakePro auxillary braking system in the RAV. To put the BrakePro in, I need to connect to the outgoing wire from the brake pedal stop light switch to the rear brake lights. The problem, there are 4 wires going to the pedal switch, black, white, gray and blue. I have determined that the white wire is the incoming 12V power. I need to know which of the other 3 wires is the 12V going out to the brake lights. (I don't want to cut them to find out.)
August 4, 2007.

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