Our Project Frontier gets gobs of attention wherever it goes. Some of our staffers think the popularity can be attributed to the high-visibility graphic treatment that Ape Wraps designed and installed for us last year (Dec. '05). Others feel the vehicle's stardom comes from the simplistic everyday nature of the buildup, i.e., bolt-on parts, and its real-world appeal as a daily driver that could hold its own on most moderate trails. Either way, nobody's arguing about the value of the $4,400 Nismo LE option package, which includes: Bilstein performance-tuned shocks, skidplates, electronic locking rear differential, foglamps, four-wheel limited-slip ABLS, six-speaker sound system, the utility bed package, and P265/75R16 BFGoodrich Rugged Trail tires.
Initially we thought the Nismo package left little room for improvement. That was until we tried to blast our way through a sandy wash in 4-Hi with the rear locker engaged. Unfortunately, the locker wouldn't turn on unless the transfer case was in low-range. This annoyed us. So we began researching why Nissan engineers designed the Frontier's (and the Titan's) rear locker logic this way. A few phone conversations later, Nissan's corporate PR representative had this to say: "Given the off-road nature of the Frontier's locking differential, we have determined it is most appropriately used while in low-range and off-pavement."
Bummed by this response, we decided to take on the task ourselves. We believed the Dana 44 under the Frontier would hold up just fine when locked in 4-Hi and even in two-wheel drive as long as we didn't try it on pavement. It's no secret that the Frontier shares a lot of internal parts with the Titan. So we poked around on Titantalk.com, a well-organized Web forum dedicated to Nissan Titans and their owners. We figured we might get lucky by starting with a Titan forum-and in fact, we did. Our search led us to electrical engineer Austin Marriage of Port Orchard, Washington. Austin had already figured out the locker override formula on his own '04 Titan. We questioned Austin about the similarities of the Frontier's electrical system. Much to our surprise, he volunteered his knowledge about the subject readily and without hesitation. A week or two later, Austin had posted a personal Web site, complete with pictures and a wiring schematic to help us complete the modification. Here is how it's done.
To perform this modification, you'll need a double-pole double-throw (DPDT) relay. These can be found at any Radio Shack (PN 275-218). You'll also need a switch of your choice, elementary wiring skills, and some basic handtools... | 
...We soldered 5-inch-long, 12-gauge pigtails to each terminal on the relay to allow for easy integration to the factory wiring harness. We then labeled each pigtail to make the process simple. |
This diagram demonstrates how to wire the relay. The numbers next to the wire color correlate to a specific pin on the differential lock control unit (DLCU) connecter plug. These are the names we wrote on the labels for each pigtail. | 
This is the harness connector for the DLCU. Use the three alignment slots to associate the top from bottom. Each pin has a number designation. It's very important to know which wire you're working with. Be sure to disconnect the battery from the truck's electrical system before starting this portion of the project! |
This picture was taken from the lower driver-side doorjamb, looking up under the dash at the area where the DLCU is mounted. The yellow arrow points to the harness plug. You'll need to remove this plug from the control unit to access the individual wires that require cutting. Be sure to double-check wire color(s) before cutting. | 
This is the color-code chart for the differential lock control unit wiring harness. |
Shown is our relay wired in. It is important to note this modification probably will void the factory warranty. | 
Once all connections were completed, we installed a simple toggle switch on the dash near the bed cargo light switch. |
With the battery reconnected we tested our modification by switching on the locker in two-wheel drive. As you can see, the diff-lock indicator lamp is on while the 4WD indicator graphic confirms the vehicle is still in two-wheel drive. | |
* Cut the [L] Blue wire at terminal 12 at the DLCU harness.
* Cut the [GR] Gray wire at terminal 11 at the DLCU harness.
* Strip the insulation from [B] Black wire at terminal 3 at the DLCU side of the harness.
* Strip the insulation from [W/G] White with Green Stripe wire at terminal 1 at the DLCU side of the harness.
* Connect DLCU side of Blue wire to relay terminal.
* Connect jumper from White with Green Stripe wire (power) to relay terminal 3.
* Connect diff-lock solenoid side of Blue wire to relay terminal 5 (diff-lock solenoid terminal 4).
* Connect DLCU side of Gray wire to relay terminal 2.
* Connect jumper from Black wire (ground) to relay terminal 4.
* Connect solenoid side of Gray wire to relay terminal 6 (diff-lock solenoid terminal 2).
* Connect jumper from White with Green Stripe wire (power) to hot side of rocker switch.
* Connect jumper from load terminal on rocker switch to relay terminal 7.
* Connect jumper from relay terminal 8 to Black wire (ground).