I think you'd do better to ask on an enthusiast's site, to be honest, but here goes...
On our car it is integrated into the engine management computer. It works off the speed pulse signal. If you were to disconnect the speed pickup then the car won't think you are moving, so the auto trans will probably throw a fit, but at least the ignition/fuel won't cut out. If you have a stick shift this will probably work. Your computer may still perform a self check and disable something or other, or switch on a warning light.
The best way to do it if that doesn't work, probably, would be to intercept the speed pulse and then build a logic box to generate an artifically slow pulse stream once you exceed a certain speed.
Some of the the reasons why cars are speed limited (1) tyres (2) driveshaft whirl (if RWD) (3) cooling system inadequacies (4) nannyism (5)handling/stability. There may be other reasons.
Your insurance will be invalid if you do this mod. Cheers
Yes, it's in the software. The ECM incorporates a rev limiter and they just set the rev limit in 3rd and overdrive to hold the cars around 108 if you have the standard 112 mph tires. Most aftermarket "powerchips" remove the governor, on the assumption that the enthusiast has already fitted higher speed rated tires, etc. These also carry the insurance and warranty void penalties that Greg mentioned, if that is any concern. About $500, not including speeding tickets.
Forgot to mention, I personally verified 108 mph as the limit in 1996 on a Hertz Crown Vic. Also accidentally determined that the maximum speed for a Radio Shack magnetic mount CB antenna was only 105 mph. It wasn't until we got reported as a "Smokey" on the CB that my wife figured out why I insisted on the Crown Vic. Never turned off the cruise control or flashed the high beams at anyone from Virginia to Florida!
