2004 grand prix alarm

Parking lights-

Not sure what is wrong, but why not switch it to negative output and use the cars neg p.light circuit? BROWN / white wire at BCM, 18 pin plug, pin 8. The BCM is just left of the steering column.   Most newer GM's can only be interfaced this way (not yours though, but I recommend it)

Also, what are you using to bypass the passkey system? Key in box, or self-learning?

When integrating with a GMSL or higher version the theft light stays on.  For that their would be instructions in the manual if its a self-learning bypass kit.  On Fortin bypasses they only bypass is the PATS-GM and with DEI they have the 556U with key in a box. You have to check your wiring with a multimeter for the lights.  And also see what kind of polarity the parking light is giving using the multi meter.  Let us know exactly what kit your using to figure this out for you.

If that happens it may be that the bypass(ring around key cylinder) may not be getting a strong signal.  It happened to me with a 03 jetta.  The light went on but car still turned on.  Make sure your ring is secure around the key cylinder.