06 FX4 5.4L 3v

I wanted to add puddle lamps with my new towing mirrors and through several threads on this site I was able to find the black/blue wire in the l/h kick panel, I tested it and had 12v with the dome light on and 0v when they cycled off. So I tapped into the wire they didn’t work, so I tested the voltage and had 12v with dome lights on and 7v with dome light off. And now my dome light and map lights stay dimly lit all the time (an obvious problem). So I removed the new circuit and reconnected the factory wire and problem remains. Suggestions/insight welcomed! Please help, thanks in advance.

 

The low voltage is a bad connection such as a grounding issue. But could be on either end.

 

I would also go with the "bad ground" thesis.

Pull your kick panels and inspect the grounding connections for loose or corroded connection or for "body rot".