Q: No GPS signal

I have three GPS units and they all work fine in all of my cars except in my 2003 Thunderbird. As soon as the ignition switch is turned on, with the engine running or not, the GPS will loose it's signal. If I move away from the car about 15 feet the signal will return but as I approach the car the signal goes away. Works great in the car as long as I don't turn on the ignition switch. I have exhausted all of my options, with no positive results. Has anyone ever had or heard of this problem? td, no ps... IPhone GPS works good, not a problem.

I really appreciate the input I have received; However, I will try and clarify some of the logistics so you may better understand the situation giving you an opportunity to give more relevant suggestions or solution to this puzzling problem. : I have three Garmin dash mount GPS units and they all work fine in other cars. :In this example the T bird is not running only the ignition switch is on. Does the same thing if the car is running.

My car has 46000 miles.
My car has an automatic transmission.