I haven't taken things apart yet but I don't see the plastic plugs in the firewall .Are they under some of the heat shield padding ?

 

Between the brake and the gas on the drivers side there is one, below the level of the brake peddle. It comes out below the steering wheel column. Yes, behind the heat shield. That is where I ran the power cable for my amp. For some smaller wires, on both passenger side and drivers there is a ball like plug (size of a grapefruit), just behind the hinges. You can work it loose and run wires around it, then seat it back in.

Oh, they are rubber, not plastic.

 

Thanks , I thought there must be some.I'm installing amateur radio gear . BTW it's best to keep such equipment on the passenger side , away from the truck's computer to prevent interference. In fact it specifically mentions this for amateur radio gear in the manual.

 

The truck's computer is on the top left side of the firewall or on the passenger side.

 

Found it ! But I was looking for a HOLE not a miniscule 3/8" hole.No more 2"x3" plug ! So I drilled it out to 5/8" for a grommet to fit the twin lead wires to the battery.
This way you feed it into the cab and into the channel below the door to the back of the cab. The other option would be to go under the cab from the battery and drill a hole in the floor or bring it in through the vents in the back of the cab.