Hey guys, got an electrical question I need help with.
1993 Ranger 4.0 XLT 2wd

I needed to pull a small lawnmower trailer recently and needed to plug in a standard 4 wire trailer light.
I purchased one of those $30 plug-n-play wiring harnesses that plug in back near the rear tail light and provide an instant means to plig trailer lights in.
I did not have any means to screw the ground in via the supplied self tapping screw and it was kind of an emergency so I carried on.
Blinkers on my truck instantly acted funny, very dim and flashed really fast. Tail/brake lights worked on both truck and trailer.
Now, two days later I've removed the harness and now my headlights will just flash on and off at random when I go to use them (they dont do this during daylight hours when I've got them turned off, but only when theyre turned on at night
I'm thinking the bad ground or too much added amperage has partially fried either a relay? or the headlight switch in the dash perhaps? I'm not a great auto electrician so could really use some advice om what to check first.
Its not fun when your headlights suddenly shut off doing 60mp in the dark. Thanks for any help.