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Trail Night Lighting System Installation
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Trail Night Lighting System Installation

Date Created: 04/21/2008
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1) Vehicle Setup

2) Performance Review

3) Installation

4) Additional Resources


This modification can be easily installed on Jeeps equipped with factory installed fog lights.* No other modifications are necessary.* No other modifications affect this install.

( For Jeeps WITHOUT factory fog lights, a switch will need to be wired into the dash. )



A trail night lighting system consisting of additional driving lights placed along side the frame rail (Fig 1) and pointing outward (to the side) is fired by a relay which is in turned fired by the factory fog light circuit.* By tying into the factory circuit (Fig 2) the system takes advantage of a fused switch already installed in the Jeep to yield a very clean and tidy install.


Once installed, turning on the night lights is a simple matter of turning on the factory fog lights.* When the factory fogs switch on they fire a second relay which then feeds power to the extra lights along the chassis.* The trail lights will work exactly as the fog lights work: they shut off when high beams are switch on, and they automatically shut off when the headlights are turned off.

Given that most trails have numerous twists and turns it was thought that the high-beams on the headlights provide negligible benefit over the low-beams since the light cannot project too far before the trail is likely to turn.* Therefore, having the night-lights tied to the fogs which necessitates that low-beams area used was deemed acceptable to the author.

This, of course, is not the case with sand dune areas where forward projection would be desirable.


The location of the lights poses some risk of damage, however, none of the authors body mounts evidenced any contact with trail obstacles and so this location should provide a measure of protection for the lights (Fig 11).* Indeed, on a recent trail run the Jeep scraped its rocker guards over a boulder projecting under the chassis with no ill-effects on the lights.* They came through without a scratch.

Wiring Integration Decision:

The goal was to utilize the OEM foglight switch while integrating with the factory wiring harness as little as possible. The theory being that Jeep does a better job of building a wiring harness to last than I do and so let's not mess it up by chopping it to bits and resplicing.

To this end the only connection to the factory wiring is one vampire clip that is snapped over an easy-to-access fog light power wire. And this only activates a secondary relay. The rest of the night lighting system operates on it's own from having it's own relay, fuse, ground points and wiring from batery to relay to lights.

On The Trail:

Often when running trails at night drivers can suffer from tunnel vision created by the headlights only lighting up what is directly in front of the Jeep.* Additionally, due to the light/dark contrast of what the headlights illuminate and what they don't, it becomes very difficult to see what is around the Jeep let alone around corners if the lights are pointing straight ahead.

The trail night lighting system simply lights up the area surrounding the Jeep greatly enhancing the driver's situational awareness (Fig 3 - Fig 10).* It also helps the driver follow the trail with some of the night lights pointing off to the side and at 45* angles.

With the lights tucked under the body there is a reduced likelyhood they will blind by-standars and other drivers. One has to get far on the side and lean down to see the glare of the lights.


Note: Refer to Figure 2, Wiring Diagram To Connect Lights

Fig 2. Conceptual wiring diagram

(click to enlarge)

Re-Using OEM Fog Light Harness:

The original fog lights on the TJ are virtually useless at projecting light out in any usable fashion.* Instead, aftermarket lights were installed.* However, the stock fog light connector pigtail was snipped off and soldered in to the new aftermarket lights.* This provided easy connection of the new lights and retains as much of the stock wiring harness as possible, including the quality factory connectors.

Mounting Lights:

Placement and mounting of the lights is the first task.* The fog light replacements on the front bumper were set at a 45 deg angle outward (Fig 1) to light up the "pocket" of darkness between the side lights and head lights.* For the side lights, two light fixtures were used on each side (Fig 1).* These are tucked up tight against the frame under the body and point outward.* The forward lights point slightly to the front and the rearward lights points slightly to the rear.* Both side lights have a very slight down-angle to project the beam under the edge of the rocker panels.* Slim profile driving lights from the auto parts store are used for their availability and low cost.

Fig 1. Lighting Placement Diagram

In this particular instance, the forward lights are screwed into the frame after placing, marking, and pre-drilling some holes Fig 11).* The location (as seen in diagram Fig 1) actually is on part of the frame that angles inward, thus pointing the light slightly forward.* The rearward side lights were mounted to the body tub in the location marked on Fig 1.* The TJ body is of double wall construction so the small sheet metal screws won't penetrate the floor.

Fig 11. Side light mounted to frame, tucked agains body

Routing Wires:

Once the lights are mounted the wires are routed.* On the passenger side the power wire drops down from the battery to connect with the first light near the body mount.* The wire then is routed through the frame rail to a hole near the rearward light to protect the wire from exhaust heat. *

On the driver's side the power wire drops down the far side of the brake booster and is routed along the hydraulic lines running against the inside face of the frame rail.* The wire is carefully zip-tied in place every few inches.

The two power wires are then routed along the top of the firewall and connected to a single wire that plugs into the secondary relay located next to the battery / engine computer (Fig 12).

Fig 12. Relay Location

From the relay location the primary power wire is routed along the wiring harness over the computer and tucking down the side to pop-up on the front edge of the battery to connect to the positive terminal.

A ground wire for the "switched" circuit runs from the relay and screws into the firewall with a sheet metal screw.

The "switched" wire is routed from the relay, following the primary wire, and along the edge of the hood to tap into one of the wires going to the front right fog light (Fig 13).* Thus, when the OEM fog light circuit is turned on, it fires the relay which turns on the side lights.

Fig 13. Tapping Into Stock Wiring Harness

Protecting Wires:

Where possible cover the wires in a protective plastic split-loom sleeve.* This protects the wires from abrasion against any sharp edges.* Wrap several windings of electrical tape around the split-loom every 6" to close it up.* It is easier to do this as you are routing the wires rather than trying to do it at the end.* The author ran out of protective split-loom and still needs to finish off the last few feet of wiring harness.


Relay Kit:

It is highly recommended to use a pre-wired relay kit with socket.* They are a few dollars more than the relay itself and provide a very good unified plastic socket rather than individual plugs for the relay (Fig 14). Unfortunately, pressed for time I simply grabbed what relay was at hand.s

Slim Profile Light Kits

Lights or lighting kits can be had from many sources.* The side lights were off-the-shelf inexpensive halogen units from Schucks and came packaged as a kit.* They have a bright bulb, good wide beam dispersal pattern, and included a nice wiring harness, switch, and connectors.* I used the wiring harness but discarded the switch.* By coincidence, the included wiring harness perfectly matched the routing needed for the Jeep.

Rear Facing Light:

Rear facing lights were not installed so as to not blind the drivers behind me. On possibility for future expansion is to wire up another relay triggered by the back-up lights and wired in such a way that when the fog lights (now night lights) come on it closes a circuit in the relay so that when the Jeep is put in revers it the rear facing Trail light comes on. But when the fogs are turned off the circuit is open on the rear lights don't come on during reverse.


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