i put new l e d lights in for signals, brake, and running lights. My headlights are normal on my 1990 defender 90. I had to get the little piece to put behind the dash in order for my new led lights to work normal. Once I finished all of the new led lights my head lights on my passenger side and running light are very very dim. What could be the issue? Switch? Bad ground? If bad ground where would
I look for that particular area? Please help. Thank you all for your time.

Also need to add when I put my head lights on the left signals don't work but the right side does.

Sounds like a dodgy earth. All you can do is trace it.