Has it always been a hassle trying to run cable thru a cable choked grommet in a firewall ?????
The cable just kinks when you try to push it thru ???
Try this solution.
Push a hole thru with a phillips head screwdriver or similar, must be round or rubber will tear.
Then find a tube of some description which will allow the cable to fit inside. ( I find an old bit of brake line to be good.)
Push the tube thru the hole you made then run the cable thru the tube.
Once cable is thru remove tube, if you did it nicely the grommet will seal around your cable.