The 12V Jumper comes straight from the battery positive post.
Since all of the "Outs" are working, it makes sense to check the "Ins." The 12V/5A Jumper is working, so take that off, test the existing power in from the Ammeter for voltage (yes, 12.2-3V), connect it to the switch (still 12.2V) and see if it delivers voltage across the switch to the accessories (no it does not). So enough continuity to read voltage but not deliver amps.
So the line from the Ammeter to the Key Switch is now suspect, or it could be further up the line (Battery/Starter Terminal to Ammeter)
