New car I bought trying to get it going, 2003 SXT.

Very potent short (always there, blows fuses immediately) on Fuse 21, ASR/FP. Checked all the wires going to the PCM, Alternator, etc, nothing mechanically wrong that I could find, all the wire looms are still in their original location and I couldn't find any wear marks.

Disconnected the 2 wire plug from alternator, both wires are shorted to the engine block, short still exists at fuse 21. Big wire at alternator still hot.

Unplugged the 3 plugs that go into the PCM with the following results:
Bottom plug unplugged (the one that goes straight up to the fuses) = no short.
Middle plug (goes to the alternator etc) = short still there.
Top plug unplugged = short still there.

I took the PDC top off and it appears clean with no corrosion.

Any ideas where I should look next?

 

If you have combed through the wires from the fuse to that PCM connector, and I mean COMBED then I would probably attack the PCM next.

 

Would that involve taking the pcm apart and looking for a short internally?

 

Probably just replacing it, if you're 100% about all the other wires.

Orrr better yet buy yourself a fuse saver and start shaking the wires/unplugging things until it doesn't trip the fuse saver.