Thanks for your quick response, Some1
I've tried to follow your tutorial to the letter, but I'll try to explain the process.
First of all, I imported the Hammer GMT models to MAX, and checked the materials to verify they were ok.
After that, I created two planes, one for each light. Each one 1x1 meter with 1x1 segments. Then I converted them to Editable Poly. Then I placed them in front of the lights objects and attached them. No rotations or any other transformations were made. Well, I've also tried to put them behind the lights but the results were the same.
In the material editor, I added a new submaterial, HAM_FLRGLOWA. Here are some screenshots to see the material properties:
And of course, I assigned the material to the planes. After that, I exported the GMTs as usual, and tested in rFactor.
Well, I think that pretty much covers all the process. Hope this helps