1990-92 Camaro Speedometer systems are different depending on model year. Speedometer malfunction or failure can be caused by a number of different causes. The most common cause is the Speedometer circuit board. This board is located in the gauge cluster near the speedometer.
The test lead locations for testing the speedometer and speedometer circuit board is shown below (plug C2, terminals 1,2,14).
Voltage is 12 volt DC. Speedometer signal is 5-12 volt DC square wave, positive bias, frequency is 1Hz and up range.
We used our Tachometer Tester, available here, to generate the signal for the test in the video below.