So I go and install a Hella 125dB air horn (08/03 production MCS). After install, "Service Engine Soon" light comes on, and stays on, even if I disconnect air horn. FWIW, it's hard-wired to the battery with no relays. WTF? Guess I'd better call the dealer tomorrow. Anyone know what's going on? Is there something that my ECU has to "learn" now? Or did I just throw the electricals a curveball? TIA