Re: odometer disable
Actually, modern automobile speedometers/odometers are all electric and as such they add no miles to the odometer when they are towed with the engine not running. I'm not sure exactly when Ford went that way, but I can tell you from experience that it was prior to 1995. I don't believe that there are any automobiles today that still use a steel "speedometer cable" like they once did.
There was at one time a kit available from Remco which did just what you are asking about. It had a solenoid that disengaged the speedometer cable when the cord for two lights was connected to the tow vehicle, but they no longer make the kit since no vehicle being towed today still needs one.
By the way, those kits were legal in all states except Oregon, because they only disconnected it when hooked up to tow.