wiring assistance

I could not find the wiring under or even near the back of my Jayco 5th wheel, so I tapped into the tailight wires with a 4-way plug. White went to ground, black to running lights, green to blinker on one side and I ran another wire to the green wire on the left taillight. I had power to the connector, but when I hooked up to my car, nothing worked.In fact when the blinker is on, the running lights also blink. I think its a ground problem, but am unsure where to even start looking. Any thoughts would be appreciated.

Thanks,
Ron