Recently put a 4 speed into my fiero. Kept the old engine wiring harness and made the necessary changes to some of the functions to allow it to start/opentrunk/reverselights. It runs good and everything functions other than the speedo. I get the code 24 on the ecm. For the speed sensor. What plug or what cables should I he looking for to find this problem?

What year is your car? Is the 4 speed an Auto or Manual? Was the 4 speed originally in a fiero? Was this an auto to manual or Vice Versa swap?

Code 24 could be a few issues.
Normal operation is VSS sends a PPM (Pulse Per Mile, which is 4000 pulses per mile) signal to the Speedometer. The Speedometer reduces the signal to a PPM/2 (2000PPM). The reduced pulse signal is then sent to the ECM and Cruise Control.

The ECM giving a code 24 means the Speedometer or the VSS is not working. Check your connections, starting at the VSS. Check the wires (purple with white stripe and a solid yellow). Check the black connector at the bottom of the speedometer.

The VSS can be removed and driven by a variable speed (0-4000rpm) drill to check for voltage. Use a volt meter set to AC-24V.

-Dave

[This message has been edited by IFLYR22 (edited 01-24-2014).]

The gear can easily fall off the VSS if removed. So when pulling the VSS try not to let it slip off.

If someone pulled the VSS before the gear might have already slipped off of the VSS and fallen into the transmission.

Yeah you can check the VSS with a volt meter but what I would do first is pull the VSS, pop off the gear, and then with the key on, spin the vss with a drill. See the speedo move up? Then it is working.

Wiring rarely goes bad at anyplace other than the connectors at the very ends, unless the wiring harness is damaged by either the exhaust or the moving pulleys/belts. The Yellow and Purple wires from the VSS run through the engine harness directly to C203 with no splices.

[This message has been edited by phonedawgz (edited 01-24-2014).]

Thanks guys! It ended up being a connection problem that was hard to see when the engine was in place. But we got it eventually!