Do you have a volt meter? Can you check for voltage at the power wire using a different ground? You might have a bad ground somewhere along the way.
If the hot wire is hot leaving the fuse box and not hot at the ash tray, at that point it would be easier to run another wire from the battery with an in-line fuse to the connector on the back of the ash tray. Then you get power all the time
While you're at it, you can run a new ground to make sure you'll get a complete circuit.