How to run a power cable through a 1996 Ford Taurus firewall

I bought a fused power cable at the hamfest in Maryland this weekend so I could install my mobile ham radio in my 1996 Ford Taurus. There was just one problem: getting the cable from the battery in the engine compartment to the passenger compartment. In between these two sections is the firewall, and the firewall on the Ford Taurus is notoriously hard to get through. Many other vehicles have unused or underused grommets that a cable can be passed through, but preliminary investigations on the web revealed only one unused grommet in the Ford Taurus, but I couldn’t even locate it. I’m writing this blog post so that anyone else who finds themselves in a similar situation will know what to do, whether they’re powering a ham radio, subwoofer, amp, whatever.

Since I couldn’t find a grommet to pass the cable through, I ended up drilling a hole through the firewall near where the gas pedal wire goes through the firewall. I chose this location to drill because it was one of the few spots that was relatively unobstructed on both sides of the firewall. I was worried about the wires potentially interfering with the movement of the gas pedal in the passenger compartment, but I came up with a solution (more on that later).

The place you want to drill through is directly to the left of the circular metal pad surrounding where the throttle wire passes through the firewall. Drill from the inside of the vehicle; the engine compartment is way too cramped. The foot well is cramped too, but doable. You’ll have to lie with your back on the lip of the doorway and your feet on the ground. I recommend using a power drill plugged into 120VAC from an extension cord. Battery-powered drills are more bulky and might not fit in the cramped space inside the foot well, and you’re going to need a lot of power to get through that firewall (you are drilling through fireproof metal, after all).

Power cable going through hole in firewall
Fig. 1: The hole in the firewall where the cable passes through. The two black cylinders contain the fuses. The hole in the insulation is a bit bigger than the hole in the metal firewall underneath, which is just big enough to fit the cable.

My power cable consisted of a red and a black wire joined together, so it was significantly larger in one dimension. Thus, I had to cut out a tall hole that would allow the wire to pass through. A neat trick is to drill two separate close-by holes with a smaller drill bit, then keep drilling with larger drill bits until the two holes merge. Then you’ll be able to fit your non-circular wire through. Also, I definitely recommend wearing a heavy duty leather glove on the hand that’s holding the drill. I wasn’t, and I left a good bit of skin on the sharp steel vent when I scraped my finger against it after the drill abruptly pierced through to the other side of the firewall.

After I bandaged myself and got the hole wide enough for the cable to fit through, everything else was easy. I wrapped some electrical tape around the power cable where it passed through the firewall to prevent wear and tear on it over time (of course, you’ll have to back out the cable a bit to do this). Routing the power cable through the engine compartment to the battery was very simple. Just go along the outside of the engine compartment above or below the air intake. It shouldn’t come in contact with anything that gets hot enough to melt it. Inside the vehicle, I used some cable ties to route the power cable underneath the console to the middle of the car so that it couldn’t get caught in any of the pedals.

Power cable routed through engine compartment
Fig. 2: The routing of the cable through the engine compartment. Notice that it stays far clear of the engine itself.

And that’s it! I now have a heavy gauge power cable going from the car battery directly into the passenger compartment, more than enough to power my ham radio and whatever other stuff I may eventually end up using. And make sure to use a fused power cable; that’s just electrical common-sense.

6 Responses to “How to run a power cable through a 1996 Ford Taurus firewall”

  1. Kelly Martin Says:

    I would, if I were you, really prefer to have an actual grommet between the cut metal of the firewall and the cable. A small bit of electrical tape won’t hold up for long in a vibration-rich environment like a car. A short here is at significant risk to cause a fire.

    Also, if you have a die grinder, you should use it to deburr the edges of the hole.

  2. Cyde Weys Says:

    Yup, I was talking to a guy on the radio earlier tonight (he’s done a bunch of car stuff) and he suggested the same kind of thing. Consider the setup right now a very temporary solution. Luckily it won’t be hard to go back and attach whatever’s necessary.

  3. Greg Maxwell Says:

    A proper grommet will also reduce the amount of fumes (think leaking exhaust gasses) that can make it up into the cabin. Clearly a good idea.

  4. Kelly Martin Says:

    I hope the fusing is on the engine side. If it’s on the passenger side and the positive lead shorts to ground, you’ll have a fire (and possibly a battery explosion) because the fuse will not protect you. If this is the case, you should insert a fuse between the battery and the point that the cable passes the firewall.

  5. Cyde Weys Says:

    I’ve since gone through and re-done the wiring so that the fuses are on the engine side of the firewall. Yay, now I have less of a fire risk. Except to rig the cable in this fashion I had to remove the T-connector from the passenger side and then crimp a new one on at the end, and I don’t have a proper crimping tool for that. So I just used pliers. It seems fine. We’ll see how it does over time.

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