No speed is shown and GPS indicator is red. Help!

Please be sure to try under the open sky and give GPS receiver up to 10 seconds to find satellites. If you are in a train, please try to get as close to a window as possible to give GPS receiver a chance to catch satellites.

If indicator shows OFF even under the open sky, please check that iPhone's (or cellular iPad) Settings>Privacy>Location services are ON. Then inside location services check that speedometer app has its location switch also in ON (Always or When In Use for iOS8) position.

In rare cases, to get GPS receiver working properly, it is required to restart the iPhone (or cellular iPad) completely by powering it down (long hold on the power button and confirm the switch off) and then on again (by pressing the power button). Then please try again under the open sky.

Please note that iPods and wifi only iPads don't have GPS chip built in and would require external GPS module for the speedometer (or any GPS) app to function properly. There are many, you can find a comparative review of two available modules here.

If none of the above helped, I have an article sharing 6 years of experience (mine and my users) with location services: https://blocoware.blogspot.com/2012/11/issue-with-iphoneipad-gps-lets-fix-it.html. The article is being constantly updated with latest information as new devices (iPhone 8/X) or iOS versions (iOS 11) emerge.