Odd electrical issue

I installed a tach that I bought from a member tonight and when I tried to start the car it just cranked....I started it yesterday and backed it in and out f the garage.
While I was trying to diagnose the issue I tried disconnecting the positive terminal and check for continuity with my test light . With the key off I got nothing but with the key in run the light was very dim....

So I trued the same test on my Barracuda.
This time with the key off the test light starting blinking as if the blinkers were on ! WTF ? I confirmed the blinkers were not on .
With the key one I got a nice bright test light.

What the hell is going on with both cars ?
Did the tac mess up my Daytona Systems ignition box ?