TBI to TPI: Fixing Speedometer & Tachometer After Engine Harness Replacement

It is a very common swap for people with TBI f-bodies to convert to TPI injection by installing a TPI engine harness. When you install the 90-92 TPI engine harness into your 90-92 TBI car, the speedometer, odometer, and tachometer no longer work. The following are instructions to get your speedo, cruise, and odometer working again.

I did a bunch of testing and looked up a spec sheet for a similar chip as the one in the VSS buffer and resolved the following:

For the VSS buffer on 1228746 and some 1227165
pin__Color__(function)
1__YEL__(VSS signal)
2__PPL__(VSS reference)

3__PNK/BLK__(Battery)
4__BRN__(GND)
5__RED__(2k ppm: output for cruise control)
6__BRN__(4k ppm: output for speedometer)
7__BLK/WHT__(GND)

To get the speedometer and cruise control to work on a 92 TBI car converted to a 1227730 ecu (or 1227749):
-remove the VSS buffer
-connect pin 5 from the VSS buffer harness connector to C1 on the 7730ecu
-connect pin 6 from the VSS buffer harness connector to B11 on the 7730

The wires from C1 and B11 go to the C207 connector and connect to NOTHING, so I cut the wires at the C207 so I didn’t have to extend them to connect to the VSS buffer connector.