LS swap electrical
The harness half of an LS swap — PCM choice, body integration, GM LAN bus, and the wiring mistakes that brick a fuel pump.
Every LS swap eventually fails at the harness. Either the fuel pump won't prime at the first key-on, the body modules can't talk to the BCM, or the PCM sits waiting for a GM LAN bus heartbeat that never came. This course is the eight-module fix — PCM choice, body integration, GM LAN bus, the fuel-pump relay circuit, and the bench-side mistakes that brick a pump before the first start.
- PCM choice + harness overviewStandalone eRod vs factory body integration, and how to read every connector cavity against the donor diagram.
- Body integration & GM LAN busIgnition switch, fuel-pump relay, oil-pressure gauges, and the LAN backbone with terminating resistors.
- A live no-comms bench drillA real swapped engine that cannot talk to the body modules. Isolate a missing terminating resistor vs a reversed CAN pair.
- Scored quiz + pinout referenceSequence the harness build without the manual and tag the diagrams that stay on the bench.
Marco runs the harness bay at a high-volume LS swap shop in the Northeast. He built his first engine harness on a kitchen table with a donor LS1 out of a 2002 Camaro, and has been chasing obscure GM LAN bus faults ever since. Every module in this track was filmed on a customer's swapped engine, with the actual donor harness laid out next to the chassis.
Every diagram on this page ships from the Torquebench resource library. Print or load them on a tablet — they stay on the bench next to the actual harness as you trace cavities and verify grounds.
The full catalog includes additional fuel-system, accessory-drive, and front-end reference sheets — unlock with the Library Pass above.
The free preview shows the first module and one reference diagram. The Library Pass unlocks every track — all twelve LS-electrical modules and every printable diagram across the catalog — for a one-time payment.
Trusted on the bench
Working-shop tech and first-time builders on what the track delivered against the actual job on the floor — accessory drives, cold-start faults, factory-diagram isolation, and the harness schematics that hit the bench rail.
My LS swap would not prime the fuel pump at first key-on. The fuel-pump relay and PCM choice modules showed me exactly what was wrong — the donor harness was missing the relay control wire I needed from the body harness. Hooked it up and the pump primed on the next key-on. The course paid for itself right there.
I had been debugging a GM LAN bus heartbeat issue on a swapped engine for a week. The body-integration module and the live no-comms bench drill gave me the exact test sequence — terminating resistor on one end, CAN pair correct polarity, ground at the right chassis stud. Fixed in a single afternoon.
The standalone eRod vs factory body integration comparison is the cleanest breakdown of the choice I have seen anywhere. The bench drill is excellent. Subtracted one star only because some of the schematic pages render small on a tablet — would help if the PDF diagrams were higher resolution for field use.
I am a hobbyist, not a shop tech, and I was terrified of wiring an LS swap myself. Marco's voice and the splice-by-splice isolation drills made the harness bay make sense — I tagged every cavity on my donor harness, completed the build, and avoided bricking the fuel pump relay. Trace, test, move on. Real skill.
Eight modules, no fluff. The PCM pinout chapter and the fuel-pump relay circuit alone are worth the price of admission. The track certificate sits next to my workbench now — customers ask about it, and I can point them to the specific module that covers the question they brought in.