Summary

The RED (Pin4 in my numbering system) wire was identified as being suitable for the purposes of connecting to the PRODIGY P3 so it can detect when the brake pedal is pressed.  This wire goes from 0V to 12.57V when the pedal is pressed.

Wire Pins Test summary.  (Details can be found in the spreadsheet)

1. BLACK goes from 0V to 12V when the Ignition is turned on.

2. PINK goes from 12V to 0V when the brake is pressed AND the ignition is on.

3. WHITE seems to change its resistance from 1.5ohms to 8ohms then settles at 1.6ohms when the brake is pressed.

4. RED goes from 0V to 12V when the brake pedal is pressed regardless of the state of the ignition

5. Blue always 12V

There was no real detectable difference between measurements between Ignition On, Engine running or Cruise control On (but not set)

Modification

This is not for the faint hearted.

First remove the plug from the socket.  There is a plastic clip that needs to be gently pushed will removing the plug from the brake switch.  It comes out easily and nothing should need to be forced.

Then  remove the tape and cloth outer cover.  

Then very carefully I removed a small section of the insulation around the RED wire using a scalpel.  This can be challenging as work has to be done in a cramped space under the dash.  Take your time and have patience. 

Once the inner conductor was bare I checked to make sure I had not damaged any of the conductors then wound around the end of a stripped piece of wire that was routed to the prodigy.

It was then soldered wrapped in tape then wrapped in the original cloth barrier.

Initial tests prove promising.  I have not yet tested behavior of the Cruise Control but suspect the other wires (PINK and WHITE perhaps) are used for Cruise control signals and independent of this RED wire.  If I discover otherwise I will update this page.