Audio Systems: Ford to Mercury radio swap, mercury cougar, ford taurus

Question
Should I cut the wires in the harness order that say "do not use for this vehicle"?

In the radio from the Taurus, there is an outlet for an additional 2-hole plug. could that be the additional ground you said I should try?
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-----Question-----
Hi. I have a '91 Mercury Cougar, and wanted to put the radio from my 93 Ford taurus in. The harnesses plugged in fine, but the radio wouldn't turn on. I noticed the gray harness on the taurus had 8 wires leading to it, and the Cougar has 6. I thought splicing the Taurus harness into the Cougar might work, but don't know what goes to what. Can you help?
-----Answer-----
This may help;
http://www.installdr.com/Harnesses/Ford-Wiring.pdf

try adding a ground wire from the radio case to a metal part of the dash first...  

Answer
The extra 2 pin plug from the Taurus was for the optional steering wheel (actually instrument cluster) volume controls.
It makes no difference when not hooked up. As for cutting any wires, it shouldn't make any difference. I would be looking more closely at if your car came with the premium sound amp(s) and if they need to be bypassed.