combining issues
 

I have an object that I'm trying to combine the parts back together. These two pieces were once together a long time ago and have not been altered in any way. I combine and merge vertices to one side and it all works out fine. I do the same to the other side and the thick border edge line remains thick after combining and merging. Both sides of the thing I'm modeling are exactly the same yet the left side merges back fine with no thick border line, and the right side matches up and connects fine but the thick border edge doesn't go away. I've checked for extra vertices that could be causing the problem I've tried just about everything I could and I still end up with this problem.

I tried explaining it the best I could without pictures. If you need to see what I'm talking about let me know and I will take a couple screen shots.

try reversing the normals on one of the pieces

if you've been duplicating and then using a negative scale on the object then frozen the transformation then that's what you need to do.

if you go Lighting > Two Sided Lighting and untick that then you'll see the faces become black on one side and coloured on the other.
this shows you the direction the face is pointing (the normal) without cluttering up the screen with those green lines

thank you so much I don't know why I didn't try that, guess I'm still rusty getting back into 3d. I checked the normals they needed to be reversed.

Yeah, don't feel bad I run into that every time I take a break and come back to modeling. I pull my hair out, cuss like a sailor, then remember to always turn OFF two sided lighting as I model. lol.