new wiring harness problems, HELP!!!

Are you running any fans off this block, 15A main fuse will blow with an 18A Lincoln electric fan running, add a 6A MSD (1A per 1000 RPM) and a 7.5A pump (fuse rated by holley) and you got close to 33A running through the main feed. That 15A fuse should be larger I would think. Check the lit switch, probably the cause (hopefully)