in most cases with the comon rubber grommets you spray the rubber grommets with a silicone spray and work them into place in the firewall then lube the wires with silicone spray and thread them thru, needle nose pliers can sometimes be a huge help
especially if the grommets pre-installed on the the cable, so you need to pull only one side of the grommet lip thru the hole, the lube tends to help ease the install...yes you need to have someone push from the other side while you gently work your edge thru and forcing it tends to rip the grommet so take your time!
btw theres some metal and plastic grommets that are inserted from both sides and rolled over on the edge with a tool that locks them into place, some are epoxied in place
heres more info
http://www.wikihow.com/Install-Grommets
http://www.milspecproducts.com/tool.htm
http://www.ch601.org/tools/firewall/firewall_grommets.htm
http://www.acehardware.com/product/...450.2628075.2628101.2628107&parentPage=family
http://www.beaconfabric.com/vindex.html?cat294.htm
http://www.milspecproducts.com/slides/phototoolszlockd.htm
especially if the grommets pre-installed on the the cable, so you need to pull only one side of the grommet lip thru the hole, the lube tends to help ease the install...yes you need to have someone push from the other side while you gently work your edge thru and forcing it tends to rip the grommet so take your time!
btw theres some metal and plastic grommets that are inserted from both sides and rolled over on the edge with a tool that locks them into place, some are epoxied in place
heres more info
http://www.wikihow.com/Install-Grommets
http://www.milspecproducts.com/tool.htm
http://www.ch601.org/tools/firewall/firewall_grommets.htm
http://www.acehardware.com/product/...450.2628075.2628101.2628107&parentPage=family
http://www.beaconfabric.com/vindex.html?cat294.htm
http://www.milspecproducts.com/slides/phototoolszlockd.htm