Home - Howell EFI Conversion & Wiring Harness Experts General Motors. GM LS-Series Products; GM LT1/LT4 Products 2014+ GM TBI Products , Inc. was formed in 1988 by Bill and Matt Howell to support the growing trend towards the use of electronic fuel injection in the Hot Rod/Street Rod and Four Wheel Drive Industries. Wiring Harnesses, ECM's, Products and accessories. TPI/MPI/LT1/CPI. GM MPIJeep · Ford · GM TPI Products · GM TBI Products · General Motors · GM Vortec Products Fuel Injection Wiring Harnesses at Summit Racing Our selection of fuel injection wiring harnesses makes it easy to bring throttle body, multi-port, or sequential multi-port fuel injection to your vehicle. Whether you’re adding an aftermarket fuel injection system to your existing engine, swapping in a completely new fuel-injected engine, or just replacing old wiring, we’ve got what you need.