SCT tuner wont power on!

check to see if anything is wrong with the port in your car, dirt,stuff like that,or try and move it side to side, maybe the port in your car is expanded where its not making a connection

Assuming that the car is a 1999-2004.

Confirm fuse F2.31(10a) in the CJB is good.

Confirm 12 volts in DLC pin #16. The wires are LG/RD. Pin #16 should be on the upper left of the connector (narrow side up).

Confirm good ground in DLC pin #4 (BK) and pin #5 (BK/YE). Ohm it out with a known good ground or better yet, back to battery neg.

Suspect that the radio installer removed/damaged ground G204 located center console very near the radio.

Ohm means to take a resistance measurement. A volt-ohm-meter (VOM) will measure the resistance to the flow of electricity. Suspect that you will find an excessively high reading indicating the ground is not good.

If you have a volt meter, most also come with an Ohm meter. Or at the very least a go/no go tester.

Optionally, measure the voltage between pin #16 and the grounds on the DLC connector. If the ground is weak, the voltage may be less than battery. The down side of this method is that it does not load circuit. A weak ground my work at very low currents but have excessive voltage drop at higher levels. This is why it is better to measure straight resistance.

Of course if the ground is missing out right, the voltage measurement will be zero thus confirming the diagnosis.