Routing wires through firewall?

I'm adding some auxiliary gauges to our '76 Comet. Water temp, oil pressure, and a tach.

I'm used to working on older cars that have a lot more room under the dash so I'm having trouble finding a place to run the sender wires through to the engine compartment.

So I'd like to hear from some of you who have done this and get a little advice on where and how you did it.

Thanks in advance.

 

I ran a 00 welding cable and some other wires through my firewall, and DEFINITELY did not want those to get cut and short out. So I went to the boat shop, got a thru-hull fitting like this... cut a hole through the firewall that would fit it, and ran everything through it. Plenty of insulation so that you will never cut through the wires. And you can cut a hole wherever you want.

Cut off any excess threaded portion that sticks out and you will only see the nut (which is on backwards in this picture) and the rounded end on the other side.

 

But where and how did you cut that hole? I can't see anywhere that I have room for a drill and I can't see where any of the factory wiring goes through or any other existing holes that I can use.

 

For the purposes of my battery relocation, I went along the passenger side.

Depending on what you are doing, you could either enlarge an existing hole, or drill a new one. Use a hole-saw made for metal.

 

thats clever. im going to have to keep that in mind. i like that more than rubber grommets that deteriorate over time.

 

For small wires, just trim the end of one of the firewall pad insulation retainers, they are rubber, and make a good grommet.

 

There's already a hole on the firewall right above where the driver-side rocker cover is. It has a rubber plug in it. What you need to do is remove the plug, enlarge the hole with a angle drill, and get the correct size rubber grommet to put in it. Run your gauge wires through that.

 

Thanks, I'll check that out. Even though this car is a 6 cylinder car, it's got power brakes and the brake booster makes it hard to see anything in that area of the firewall, but I'll see what I can find.