Ok, so it seems the luminosity of the surface needs to be set to 100%. I did this, and now the surface shows as textured and not black.
In the textname.h class, it lists all of the textures in the game. In ha_mfd.c it shows there that the texture to be used for the CRT is called TEXTURE_INDEX_HVCKPT_DISPLAY_CRT. I tried changing the texture to TEXTURE_INDEX_HAVOC_TRQ_GAUGE, the texture file is called HAVOC_TRQ_GAUGE.bmp. But when I try to go into the cockpit in the game, it just crashes out to desktop. My idea was to try and get the main CRT to display on this other texture.