I am trying to help a friend of mine trouble a GPS issue with his vehicle ... 2003 GMC Trailblazer....

He original puchasing a Garmin Nuvi 220 and installed it in his truck... while the truck is not turned on (key off), the unit find the GPS signal and work flawlessly. Once he turns the key to the on position (vehicle not started) the signal instantly is gone. I even tried the same thing with my Garmin 76Cx... same thing.

He got in touch with Garmin and they recommended going with a Nuvi that has the ability to use an external antennae. We have done that and still even with the external antennae, same thing, signal gone when the key is turned to the on position..... we have tried various mounting locations for the external antennae, roof, hood, above the back hatch....

Any ideas?