2002 GMC's horn works. Swap Pontiac's horn with GMC. Both horns work on GMC. Both fail on Pontiac.
Attach test light to the two contacts on the Pontiac horn harness. Press steering wheel, test light illuminates.
Attach jumper wires to horn and battery. No honk. Try same test with GMC horn. No honk. Try both with reversed polarity, still no honk. Try all of that again at the definitely charged battery in the GMC in case the one in the Pontiac's battery is lame or I'm not getting a good connection. No honk. Disassemble one horn partially to get better contacts to connect jumper wires. No honk.
De-pin Pontiac harness horn connector. What comes out is two perfect metal slide connectors that can still be used without the plastic/rubber stuff; they will slide right on to the horn's simple solid pins. Test again with test light to be sure; still good. Try on each horn, still no honk.
Ok, so maybe these aren't traditional horns, but just dumb speakers and the PCM supplies the tone. That would explain why testing them with jumpers on the battery fails, though it wouldn't explain why the Pontiac's harness illuminates the test light. So I look it up in the OEM service manual...nope. The "Description and Operation" section seems to support it being a traditional horn that just takes plain 12v, and the diagnostic tests include my jumpers-to-battery test.
WTF. Maybe something is somehow wrong with the circuit that it can illuminate a test light, but can't move enough current to honk? What about being unable to make either horn honk by applying 12v directly to them, when I know that the horn circuit on the GMC can make both of them honk?
Maybe I'll buy a brand new horn and wire up a relay. Should a Grand Am horn play Dixie?
