GMPP LS3 E-Rod Harness - E-Rod Wiring 101

You can hide as much as you like, but we opted to keep it simple and mount everything underhood since all of the E-Rod components have been approved for that. There are two connectors, however, that must go inside the cab: the drive-by-wire pedal plug and the OBD2 port. We like to create as few new holes as possible, so we enlarged the original gas pedal mounting point just enough to wiggle them through.

Take this group of four wires, for example. The coolant, generator, cam, and mass airflow (MAF) sensor will run down the driver side of the engine.

Once you’ve got your basic battle plan, transfer the bundle onto your windshield with the wires still grouped basically into left and right bunches.

Those plugs are far too big for a suitably sized grommet to slide over, so to take care of that rectangular hole in an oddly shaped location we decided to fab our own grommet clasp from some scrap sheetmetal.

The coolant sensor is located on the front of the driver-side cylinder head. This is critical for E-Rod emissions compliance; the ECU controls the electric fan through this sensor and is set to turn on at 207 degrees F.

The two sides slide together to capture the grommet and even reuse the original screws and holes from the gas pedal mount. If you’ve got a bead roller, you can make a bevel that will allow the two pieces to sit flush, otherwise a good bead of gasket maker between the clasp and firewall will seal it nicely.

The cam sensor uses a specific pigtail from GMPP to adapt from the E-Rod harness to the sensor on the LS3 located down by the dampener. The pigtail should be in a separate package of sensors included with E-Rod packages.

If you’re using a GM alternator, you’ll plug this four-pin connector directly in, however, if you’ve opted for an aftermarket one-wire alternator that is self-exciting like our PowerMaster unit (included in the Eddie Motorsports accessory drive), this plug won’t be used. Our sources at GMPP say there shouldn’t be any issues with trouble codes by doing this. All we need to do here is run a wire directly from the terminal on the alternator to the battery; the capped-off plug on the PowerMaster is nonfunctional.

Aftermarket accessory drives that move the A/C compressor up to the top of the engine for clearance will probably create a fitment issue for the purge solenoid for the evaporative emissions canister. No sweat: We used a piece of scrap sheetmetal to create this simple bracket that raises the solenoid up about � inch and rearward about ⅜ inch.

Speaking of the back of the engine, the oil pressure sensor tucked in behind the intake manifold is an easy one to miss. The red cap in the background is a vacuum port we’ll use for the brakes.

Due to varying engine bay configurations, the air induction and MAF sensor mounting are up to you. The basic specs are that the tube needs to be 4 inches in diameter with a minimum straight section of 6 inches. The MAF sensor itself needs to be mounted in the middle of the straight section of tube, but at least 10 inches from the throttle body and in the correct orientation. It’s not as hard as it may sound, but it is important to get correct. Want to see what we did? Check out PopularHotRodding.com or our Facebook page for the web exclusive story.

The solenoid has a tab on it that will grab the outer edge of the bracket, so once you run a bolt through it there won’t be any movement. The bright red and blue plug for it is hard to miss.

There are three ground wires on the main harness bundle: one on the passenger side and two on the driver side. Make sure to provide a clean surface for ground and also ground-strap the engine. We’ve seen plenty of ECU issues that were traced back to floating grounds.

In the same bundle of wires as the evap solenoid plug is the electronic throttle-body plug. There’s no way around it for emission certification—the factory drive-by-wire throttle body must be retained.

Our original A/C box was severely damaged and all the components inside needed to be replaced, so we opted to delete it, which also created a nice mounting location for our E-Rod ECU on the firewall. If you mount it in this configuration and allow the harness to loop over behind the wheelwell, the three large ECU plugs will line up perfectly. You can mount this inside the cab, but it’ll take a significant hole to slide the three large ECU plugs through. If you have an original style box, go with a low mount under it or on the wheelwell.

Over on the passenger side, the manifold absolute pressure (MAP) sensor also has a specific pigtail that should be in the bundle with the various O2 sensors.

Along with the O2 wires, the two knock sensors (one per side) and the crank position sensor drop down behind the engine and plug in at the rear of the block behind the engine mounts. The wires are wrapped for heat resistance, but be sure to route them away from the exhaust manifolds anyway.

The E-Rod ECU doesn’t come with mounts, so we used these spare vibration isolators we had from an MSD ignition box. We love these things; you can get them straight from MSD and tons of them are on eBay. Electronics-style vibration mounts will work as well.

We’re planning to move the EcoNova’s battery to the trunk, so the original location made the perfect spot for the fuse and relay box. These boxes have only one tab for mounting; we used a 2-inch piece of tube as a spacer and a long bolt to mount it directly to the wheelwell. We’re still debating on whether we should figure out a way to secure the other side. Running up into the fender is the bulkhead for the transmission (more on that in a later issue), as well as the gray fuel pump wire and blue fan wire. Both are relayed in the fuse box and must be connected directly to the power side of the pump and fan respectively, or else trouble codes will be triggered.

There are plenty of ways to mount the pedal; our solution is to use heavy-wall tube leftover from control arm fabrication to space it out from the firewall a couple inches. Once we’re happy with the positioning, we’ll weld the tubes to the stock pedal bracket and tie them together with a plate for extra strength.

Along with the accelerator pedal plug, two additional wires need to be integrated under the dash. The red ignition switch wire should be tapped into the ignition harness for keyed 12 volts. On older GMs this will be a thick orange wire. The gray MIL wire is the trigger for the check engine light. It supplies the ground for the circuit when triggered. We’ll probably tie this into a stock idiot light, though we’re tempted to put in an actual check engine indicator. The OB2 port just needs to be accessible, so anywhere under the dash is fine. We’ll likely mount it on the backside of the radio.

The drive-by-wire pedal needs to be mounted to the firewall, but it’s unlikely to land exactly where you want it. GMPP recommends a 2-inch height difference between the brake and accelerator pedal to account for brake pedal travel. The accelerator only needs .75 inch of travel to be at WOT.

So there we are, our E-Rod engine is roughly 75 percent wired. We just need to integrate a few systems from the EcoNova’s original harness and run a wire for the fuel pump. What’s the other 25 percent? You’ll see that when we swap in the GMPP SuperMatic trans and controller in an upcoming issue.