I'm not sure if you have this or not but I've installed many systems with my brother and we always used 12 THHN electrical wire as a snaking tool works every time.
I installed new wiring for my speakers as well and I used a 4-conductor 14 gauge wire.
Take a piece of the THHN about 4 feet long so you have plenty to work with. Cut the end of the piece at an angle, so it forms a point. Now from inside the car push the wire through and with your other hand fell the grommet inside the door. You'll feel the wire trying to poke through the grommet in the door. Now if you have fingernails just pick away at it until the wire pops out. Doing it this way allows the grommet to still seal up rather well. Then just tape on the new speaker wire and pull it through very slowly so as not to brother the other wires in the sleeve.

I have pictures if you need them. Just let me know.

 

What's THHN?

I got one speaker in but the other grommet is impossible.

 

Hummm.. Well its electrical wire mostly used for commerical electrical applications but its makes a great flexible snaking tool you can get it at almost any hardware store. Just make sure to get 12 gauge, and get some color other than black if you can. So when it pushes through the grommet you'll be able to see it.

Home Depot and Lowes has it by the foot.

Which door did you get wire already?

 

Someone recommended using a large size nylon cable tie, as a flexible and non-sharp (won't puncture the rubber tube) snake. I am too lazy to do a search. I followed that advice and it worked like a charm. The cable tie comes pre-equiped with a hole through which you can fasted the wire you are pulling. Contrary to what seemed to me common sense, it turned out to be easier to work from the car to the door.

Good luck - not a big job - no need to sweat it.

 

If you go the route of lubing your snake and wires, you may want to try something like KY. Vaseline or baby oil are petroleum based, so they won't evaporate and just hang around collecting dirt and grime. KY is water based and will evaporate, leaving clean wires in your grommet.

 

The above is a good point because both Vaseline and baby oil will sit on the wires and begin to errode them our time. However you really shouldn't need any, mine went through no problem dry.

 

I didn't even need a snake to get the wires through the grommets, the problem is getting the grommets through the doors. One's down, I just need to keep working at it to get the other through.. the passenger door is the one that's left.

 

Alright alright, I finally got the other grommet in.

THE TRICK IS... to pinch down the side of the grommet that sticks out more and put it through the hole STRAIT ON (no angle) then just push and pray.

 

I never even took the grommets out

Good job!

 

I use my spray silicon gotten from local dive store - it contains nothing but pure silicone as it is meant to treat scuba equipment that you have in your mouth - just spray some in your palm and slide wire through - what can be as harmless or what can as easy to use - not greasy, no harmful residue and good to lubercate any rubber, etc in future.