Installing Above-Cab Auxiliary Lights

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By Michael Zimmers

There’s something about trucks: they just seem to cry out for upgrades and accessories. Whether it’s better mechanical parts, a sophisticated sound system, or exotic electric accessories, it seems that high-quality accessories add to the enjoyability and value of the vehicle.

One accessory with a lot of "sex appeal" is auxiliary lighting. I’ve long admired the gleaming chrome lamps I’ve seen on various off-road vehicles, and wanted to put some on my ride, "just because." Unfortunately, this was complicated by the fact that my truck, like many late models, has no rain gutters on the cab, and so, no way to mount a light rack. No rack, no lamps…or so I thought.

Using a cab guard as a light bar

One of my recent projects, which I outlined in this article, led me to a company, Highway Products, makers of heavy-duty truck storage solutions. One of their products is a cab guard, which protects the cab’s rear window from rack-carried supplies. This particular cab guard has a flat, horizontal aluminum brace at the top; it occurred to me that this horizontal piece would make an ideal mounting point for lights.

Pictured here is the cab guard with one of their saddle-style tool boxes (this picture is not of my truck). Highway Products’ products are very well built. Their boxes use thicker material than any other I’ve seen, the construction is first-rate and the finish is absolutely gorgeous. It’s evident that the company has a lot of pride in what goes out their doors. The cab guard is certainly no exception: it fit my truck perfectly and was quite simple to install, though my already having installed one of their tool boxes did add some effort to the installation.

Selecting a lamp supplier and lamp

Anyone even slightly familiar with the truck accessory market knows that there is a lot of choices for auxiliary lights. After reviewing the alternatives, I chose PIAA for this project. PIAA enjoys a solid reputation for quality, has a nice selection of lamps, sells ready-to-install kits, and has an excellent web presence. After a brief discussion with their technical support department, I decided to go with two pairs of their 520 SMR series lamps. These lamps provide plenty of light, are attractively finished without being too gaudy, and appeared to be the correct size for my truck.

On the subject of size…

This is probably a good time to mention that I didn’t want this project to prevent me from being able to garage my truck. As I only had about six inches to work with, and I needed to be sure that my selected components didn’t stick up too high. Fortunately, both suppliers were able to furnish line drawings with exact measurements that enabled me to be sure my design wouldn’t result in an unfortunate meeting of lamp and garage door.

Installing the cab guard/light bar

The cab guard is really quite simple to install. It comes pre-assembled from the manufacturer, and includes mounting hardware. Rather than detail the entire installation, I’ll just share a couple of points

Possible snag:

Highway Products furnishes cap screws to mount the legs of the guard to the bed rail of the truck. If your truck bed is designed to allow access to the underside of the rails, great; if not, however, you’ll need to use sheet metal screws. I strongly recommend self-tapping screws, such as the Tek® style.

The use of sheet metal screws can be further complicated if your bed rails (like mine) are made out of composite, rather than metal. The composite material is not strong enough for a screw-in fastener, especially for something like a cab guard that could apply a great deal of leverage to the mounting points. Fortunately, about 1 1/2" below the composite is a steel member which will accept a self-tapping screw.

What this means, though, is that you’ll need a pretty long screw. My screws had to go through the tool box (sitting on top of the cab guard legs), the cab guard legs, the top of the bed rail cap, and down to the metal. This necessitated a 2 1/2" screw. You will find that these aren’t particularly easy to come by, especially with a hex head and in size 1/4" or #14. I had to special order mine.

If you choose (as I did) the cab guard model that includes integrated turn/brake lights, you’ll need to splice the wiring into your vehicle’s taillight wiring. There are a couple of options for this. Highway Products’ installation instructions suggest that you leave this step to an authorized service dealer. You can, however, try it yourself. I accessed the wiring at the trailer light hook-up. On other vehicles, it may be preferable to splice directly into the taillight wiring. Be aware, though, that doing this yourself may void your warranty on the vehicle’s lighting system, so proceed with a bit of caution.

If you choose to do this wiring yourself, it’s best to run the wires from the cab guard through the access holes in the front of the bed, down through the frame rail to the trailer electrical hookup at the rear. I discovered that there was barely enough wire to get the right side connected, and mine is a short-bed truck, so depending on your model, you may need a splice to get the extra length you need. Highway Products is now aware of this issue and will be shipping new units with longer wires.

Here’s a picture of the cab guard, taken from the rear of the truck and overlooking the tool box. Even though the guard’s mesh looks as though it would impair visibility to the rear, I have found this not to be the case.

Installing the lamps – mechanical

The mechanical installation of the lamps is quite simple: just measure and mark the desired mount points across the top of the cab guard, drill holes for the mounting bolts, and install and tighten. (After my installation was complete, I decided that I needed a little more clearance for the light beams over the cab, so I bought 3/8" thick nylon spacers and reinstalled. The need for this will depend on your particular model of truck (as well as the model of lamps).

Possible snag:

The lamps are equipped with metric M10/25/1.50 bolts for mounting. These bolts are adequate for mounting the lamps to a relatively thin surface (such as mounting tangs on a bull bar), but the top piece of the cab guard is an inch thick, and the spacers added another 3/8", so I needed considerably longer bolts. I found some M10/50/1.50 at my supply store easily enough, but if your supply store isn’t very well equipped with metric fasteners, you may have to substitute an SAE fastener. I’d guess that a 5/16" or 3/8" would be equivalent.

Here’s a photo of a couple of the lamps installed. You can see the white nylon spacers between the lamps and the top of the cab guard.

Installing the lamps – electrical

Possible snag:

The lamps are sold in complete kits, including relays, remote switches and all necessary wiring. "All necessary wiring," that is, if you’re planning on mounting your lamps within a few feet of your power source. This happened to be true in my case, but only because the tool box sitting next to the cab guard contains a bank of batteries. If you’re planning on a similar lamp installation, but intend to run it off of starter battery power, you’ll need to splice the wires that run to the lamps. In my case, I had to splice the wire to the on/off switch.

Once you’ve resolved any wire reach issues, the first step is to mount the relay. The relay is sort of the hub of the wiring system: it connects the power source (the battery), the grounds, the lamps and the on/off switch. I mounted my relays inside the tool box, against the forward wall. This was extremely convenient for battery and ground hookups.

I then drilled a 1" hole a few inches under the relay to feed the lamp wires through. The reason I needed such a large hole was due to the rather large connectors that PIAA uses. I could have gone with smaller holes and put quick-disconnects in the wiring, but it didn’t seem necessary. I used a hole cutter to make the holes, as I’ve discovered that drilling large holes with a hand-held drill and conventional bit is rather challenging. I also put a grommet around the hole to further protect the wiring going through it.

Once this 1" hole was drilled, I fed the wires out, ran them up the side pieces of the cab guard, and across the top member to the lamps.

The final piece of wiring was the on-off switch. The kit includes about 6′ of wiring, which would ordinarily be enough, but was far too little for my particular application. I bought about 25′ of 18-gauge, 2-conductor wire and ran it through the 1" conduit (from Electri-Flex Company, installed from a previous project) that runs along the right frame from bed to engine compartment. As a side note, if you’re running wiring, for any purpose from engine compartment to bed, I’d urge you to take a close look at the products offered by Electri-Flex Company. It makes wire routing much easier and keeps the wires safe.

Here’s a picture of the conduit exiting the bottom of the tool box and passing through the right access hole at the front of the bed.

Once in the engine compartment, the conduit stops and the wire is protected by split-loom tubing for the rest of its run to the large access hole in left side of the firewall. Here’s a picture of the firewall hole with the rubber plug still in. The on-off switch wiring is small enough that I was able to pass it through this hole and still keep the plug in, which is nice. The actual wire is hidden here by the black split-loom tubing you see in the upper-right corner of the picture.

Note: there is a third wire coming off of the on-off switch. This supplies power to the switch, and is supposed to be tied to your vehicle’s headlamp wiring, so that the auxiliary lamps can’t be operated without the headlamps. I bypassed this (mostly out of lazyness) and just tied the third wire to the battery, so my auxiliary lamps operate independently of my headlamps.

Once the wire is through the firewall, it’s relatively easy to bring it forward to the dashboard. Since I like my projects to be as reversible as possible, I decided not to drill a hole in the dashboard for the wiring, instead opting to bring it out through a crack between trim pieces:

PIAA kindly includes some very strong double-sided tape to fix the switch in the location of your choosing.

Aiming the lamps

Once the installation is complete, the only remaining task is to aim the lamps. In case it needs to be pointed out, lamps such as these are strictly for off-road purposes, as they could easily cause momentary blindness to oncoming drivers. As such, aiming them is pretty much a matter of personal preference. I chose to aim mine as low as possible while still clearing the cab, and straight ahead. This gives me a smooth blanket of light about 100′ to 200′ in front of the truck, which is plenty of distance given the speeds at which I expect to travel while off-road. One option might be to turn the outer lamps outward a little, to give more side lighting, or to aim them slightly higher, if you wish more forward vision.

Here’s a picture of the finished product from the front of the truck. As you can see, the lamps, while prominent, don’t stick out like sore thumbs. The installation is relatively subtle and very tasteful.

So…do they make a difference?

In a word: abso-freaking-lutely! The pictures I took simply don’t do justice to the amazing difference in visibility, clarity and ease on the eyes that I experienced with the PIAA lamps. As mentioned above, I trained my lamps downward for short-range illumination, so the photos don’t show the lamps’ potential to light up waaay down the road, but trust me…it’s there.

This pair of photos was taken in a very dark residential area, on a street that goes down a gentle grade. While the difference here isn’t too obvious, notice that the OEM lamps by themselves only light up a small strip in front of the vehicle, while the PIAA lamps widen the area of visibility (you can see some lettering on the road surface with thse lamps on). The PIAA lamps also are a lot brighter, though the photos don’t reflect it.
These pictures are on a flatter (and straighter) roadway. The PIAA lamps greatly add to the depth of good vision, as well as raising the "bright line" up to eye level, as evidenced by the reflective road markers visible in the picture to the right.
How the lamps perform on the roadway is interesting, but these lamps were intended for off-road use, and it’s there where their benefits really, um, shine (sorry). With OEM lamps only, the fender-high weeds block the visibility past about 10 feet, a frighteningly short field of vision no matter what speed you’re travelling. The PIAA lamps provide a carpet of light that goes (I’d estimate) 200 feet or so, and could be more if I positioned them differently.
Here’s another off-road comparison, this one in even taller brush. Again, the field of vision is deepened greatly by the PIAA lights. The dark band between the two lighted areas is a shadow created by the tall weeds just in front of the truck. I’m not sure how any lights could obviate this; perhaps more creative directional positioning might do it.

Obviously, the PIAA lamps here, mounted on the Highway Products bar, provide a significantly safer driving experience in any terrain that can even partially block fender-level lamps. This is the improvement that I was really hoping for, and is what makes the investment so worthwhile.


I’m really quite pleased with the way this project turned out. The installation was smooth and uneventful (and would have been even faster if not for my already-installed tool box). The products I selected are of excellent quality and work well. And my truck seems even safer with the added lighting. I’d recommend this project for anyone who wishes more light for their off-highway night driving.

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