Installation Tip:
Running Wires Through The Firewall

We have all had a vehicle or two that was difficult to get through the firewall. Today we will show you a few tricks we have learned that can help make the job go quickly.

Modern firewalls can be very cramped. Start off by looking for an existing place to pass the wires- Try the grommets of the main wiring harness, the emergency brake cable, and the hood release as starting points. Don't forget to look for useable grommets on the passenger side of the firewall. If you can find and use an existing grommet, this is usually the best way to go. Simply poke a hole through the grommet with a metal hanger. Tape the wires you wish to pass through to the hanger- and pull them through the other side with the hanger. Be cautious of rubber tubes without wires- they are often drainage conduits or vacuum lines. Puncturing them can cause water leaks or other vehicle damage.

Often it will feel that there are so many accessories bolted to the firewall you will never got through it. Rather than grommets there are sometimes plugs in the firewall which are almost impossible to go through. Instead- go around them: In many vehicles the rubber boot between the body of the vehicle and the door is readily accessible from inside the vehicle and in the doorjamb. Simply pull the boot back into the door jamb area for easy access. Make a ¼ inch slit in the grommet with a knife, being careful not to damage any wires within. Pass your wire through the slit in the boot into the vehicle. The remaining wires (still in the doorjamb) can then be "fished" to the front of the vehicle, where you will almost always find an existing hole in the fender to enter the engine compartment. Seal the rubber boot back with a thin layer of RTV, allowing it to "set" with the door open so that the flexibility of the boot is not compromised. Another tip: If the slit in the boot is made on the bottom towards the front of the vehicle, no cosmetic changes will be detectable with the door open. Before taking this route make sure that there are holes in the fender which are accessible, and that the wires being passed through cannot slip into the wheel well or become entangled within any moving parts.

In some cases going through the doorjamb or firewall can be next to impossible, even with the above techniques, and that brings us to drilling - which should be used only as a last resort. Look at the firewall and floorboard thoroughly before deciding where to drill. On many cars you will find a metal plate where a clutch linkage would have been installed had the vehicle been manual. Clutch plates are often one of the easiest places to drill as you can normally see both sides of the plate. Unless there is an obvious location to drill through, such as the mentioned clutch plate, we suggest drilling on the downward side of the firewall where it meets the floorboard. This will reduce the likelihood of damaging vehicle components, as you will be drilling away from them. A few other pointers when drilling: Always "center-punch" wherever you are going to drill. If you can not see the punch mark on both sides- DON'T drill. Only when the mark is visible in both sides will you know exactly where (and what) the drill will penetrate. Be extra cautious when drilling- the modern firewall is full of potential hazards, ranging from simple vacuum lines to 1000+ dollar computers. Also- Your firewalls "new hole" will have very sharp edges. It is always best to insulate wires passing through metal holes by installing a plastic or rubber (best) grommet, which will help prevent leaks and damage to the wiring.