What is needed to bolt a TH400 to an LS engine and get a VSS signal to the PCM in a C10?

Here is what the documentation says. Each point links to its source; details depend on your exact computer, harness and transmission.

Tach and speedometer signals

• LS Control System kit: The ECM is programmed to expect 40 pulses per revolution from the VSS, typical of automatic transmissions. (Chevrolet Performance)
• LS Control System kit; 4L60 / 4L80: The LS Control System harness is designed to plug into the output speed sensor of 4L60 and 4L80 transmissions, which have a 40-pulse output. (Chevrolet Performance)
• late-model GM automatics: Late-model GM transmissions used an internal speed sensor outputting 128,000 pulses per mile. (Dakota Digital)
• The SEN-01-128 is NOT for use with transmission shift computers or ABS systems. (Dakota Digital)
• Sources differ: Conflicts with the Dakota Digital product page, which calls the SEN-01-128 output a direct replacement for the stock GM internal speed sensor for ECM use.

Transmission control

• Lokar's TH400 electric-kickdown instructions (INS0004, Rev. 05/08/14) are designed around the Lokar SRK-4000 carburetor bracket/return-spring assembly; a cable-operated switch box mounted under the transmission trips at WOT and energizes the detent solenoid, and the switch-box wiring is not polarity-sensitive (either wire to either terminal). (Media)
• Lokar mounts the TH400 kickdown switch box under the transmission with 5/16-18 x 1.25-inch bolts and 1/4-inch spacers, cuts the cable housing to the bracket-to-bracket distance plus 1 inch, and adjusts at WOT with the inner wire pulled tight: the throttle must reach WOT without interference and no cable slack may remain at WOT. (Media)
• Lokar notes the TH400 detent solenoid may have one or two terminals, and recommends leaving about 1/2 inch of excess inner wire beyond the stop for future adjustment. (Media)
• Lokar's TH350 kickdown bracket installs under the two rear driver-side intake-manifold bolt heads, with the cable housing snapped into the bracket's square opening; proper adjustment lets the engine reach WOT without cable interference while the cable cannot be pulled any farther at WOT. (Partsgeek)
• Lokar's universal TH350 cable adjustment procedure: release the housing latch, hold the throttle at WOT, and relock the latch. (Partsgeek)

Confirm against the instructions for your exact parts before wiring. More: Tach and speedometer signals in our tuning guide.