If anyone is interested, here is how to modify the original circuit with a on/off switch to toggle the bypass valves between normal and always open.
Material Req'd:
one 12 Volt Automotive Relay
two insulation displacement connectors
one toggle switch
one 5 watt, 500 ohm resistor (may not be...
Ahh ... got it.
Well, the simplest way to keep the valves open at all times is to disconnect the vacuum lines from the exhaust bypass valve actuators at the two silencers. Plug the lines with a golf tee or something similar to prevent a vacuum leak. The valves will revert to the open position...