The 2017-2019 Duramax L5P Derringer install is straightforward, but the details matter. This system ties into the T-MAP and fuel rail pressure sensors, then routes the starter cable into the cab for iDash connection and control. The big thing to get right is termination. The termination cap at the Derringer and the termination jumper at the back of the iDash tell the system where the circuit ends. Leave either one out and you can get odd behavior. From there, it comes down to clean routing and secure mounting. Keep the harness off moving parts, mount the module on the crossmember with the LED facing forward, and choose your starter-cable path based on what matters most to you: the firewall route gives better protection from the elements, while the fender and door-jamb route is easier. When it’s installed correctly, the Banks Derringer Tuner and iDash make for a clean, removable L5P setup with added power and in-cab visibility.
This installation covers the Banks Derringer for the L5P with an iDash 1.8. The video begins by introducing the Derringer Gen 2 module, which uses a new housing but retains the same calibration and performance as the original Derringer. Installation is also unchanged, so the procedure applies the same way as with the earlier unit.
Before installation, the kit components are identified, with special attention given to the termination hardware. If the Derringer was purchased with a switch, the system uses the gray termination cap. If it was purchased with an iDash, it uses the black termination cap. The video explains that the termination cap and the termination jumper on the back of the iDash both contain electronics that tell the system where the circuit ends. In practical terms, they function as the endpoints of the network. If either the termination cap or the termination jumper is omitted, the system may behave unpredictably.
Because the work is being performed on vehicle electronics, Banks recommends disconnecting the batteries before starting. On the L5P, that means disconnecting the negative terminal on both batteries. The new Rev C harness connects at only two locations on top of the engine: the T-MAP sensor, identified here as the temperature manifold absolute pressure sensor, and the FRP sensor, the fuel rail pressure sensor.
To disconnect each factory connector, the gray locking clip on top of the plug is first slid back slightly, about one-eighth of an inch. Once the lock is released, the connector can be pinched and pulled away from the sensor. The video emphasizes pulling on the connector body rather than the wires, and notes that a slight wiggle may help. The same process is used on both the T-MAP and FRP sensors.
With the factory connectors unplugged, the Derringer harness is connected inline. The lead marked MAP is attached to the MAP sensor connection, and the FRP lead is connected at the fuel rail pressure sensor. After both inline connections are made, the locking clips are slid back into place on the plugs.
The harness should then be secured with zip ties and routed across the top of the engine so it cannot interfere with moving parts. From there, it is routed toward the battery area and ultimately to the crossmember above the battery. Once the harness is in place, the Derringer module itself is connected to the harness.
After the module is connected, the correct termination cap is installed on the Derringer: gray for switch-equipped kits and black for iDash-equipped kits. The starter cable is then attached to the other side of the module. The video cautions against forcing the connector into place because the pins are gold-plated and can be bent. Both the termination cap and the starter cable have locating tabs that align with matching features in the Derringer, so each connector fits only one way. Once aligned, the connector slides in smoothly and is secured by turning the locking mechanism.
The Derringer is mounted on the crossmember with the LED facing toward the front of the vehicle so it remains visible when the hood is open. The housing includes small openings that allow zip ties to pass through for secure mounting. Before moving on, the harness routing is checked one more time to confirm that it is clear of moving components, the battery tray, and any other parts that may need to be removed or serviced later.
The next step is routing the starter cable into the cab. The video presents two methods. The traditional method passes through a large firewall grommet, while the alternate method routes through the fender and then through a small grommet in the driver-side door jamb. Banks recommends watching the full explanation before choosing a route.
For the firewall method, the starter cable is pushed through the large bulkhead grommet into the cab. This can be done alone, but it is easier with a second person inside the truck to locate and pull the cable through. There are two ways to get past the grommet: either cut a hole in the grommet and use a coat hanger or similar fish tool, or push the grommet down and route around it, as shown in the video. Inside the cab, the plastic cover above the driver's left foot is removed by releasing one clip on the left and two on the right. The cover then pulls outward and drops down, allowing access to the area where the cable comes through. The starter cable can then be found by hand and pulled into the cabin.
The alternate route is easier but leaves the cable slightly more exposed to the elements. For this method, the cable is passed through the fender using the hole furthest from the hood hinge so it will not be pinched. It is then routed back toward the driver's door and passed through the 1-inch-tall round grommet in the door jamb after a hole is made in that grommet. From behind the dash, the cable can be reached and pulled through into the cabin.
Once the starter cable is inside the truck, the side dash panel that covers the fuse block is removed. This panel is retained by clips and can be carefully pried away. The starter cable is then routed up and over the emergency brake and snaked along the side of the dash toward the A-pillar or wherever the iDash will be mounted.
The OBD cable is plugged in and routed along the same path as the starter cable. The two cables are then bundled together with zip ties. Any excess length is looped, secured with zip ties, and stored behind the side dash panel area so the installation remains tidy.
If the kit includes an iDash and a pillar mount, the factory A-pillar trim is removed next. Two plastic covers conceal the 10 mm bolts that retain the stock pillar. These covers can be removed with a screwdriver or plastic trim tool, taking care not to damage the trim if it may be reinstalled later. After the bolts are removed, the pillar is pulled toward the steering wheel and then upward.
A small white plastic nut must be transferred into the new pillar mount. It is inserted into the center of the elongated slot at the top of the pillar. The wires are then fed through the gauge opening, leaving about 4 inches exposed. The pillar is pushed down into place at the dash, and the weather stripping is pulled out and around the pillar to help hold it while the fastener is started. The screw is then threaded into the plastic nutsert by hand and tightened with a screwdriver until snug. The video specifically warns not to overtighten it, since the nut is plastic and can break.
Before inserting the iDash into the pillar, the termination plug on the back of the gauge must be verified. If multiple iDash units are installed, only the last iDash in the chain should have the termination plug. With two iDash units, the plug belongs in the secondary gauge. With three, it belongs only in the third gauge. The two white plastic nuts and the black plastic spacer on the back of the iDash are removed and not reused for this installation.
The cables are connected to the iDash, and the gauge is carefully slipped into the pillar mount. The fit should be tight enough that the iDash stays firmly in place. If the firewall routing method was used, the black plastic footwell cover removed earlier is reinstalled. The installation concludes back in the engine bay by reconnecting both batteries. At that point, the Derringer and iDash installation is complete and the truck is ready for use.