Ammeter grounded out.
Ok the very first thing we need to know is "what year make and model" are you working on, because I doubt it's a hemi powered Farmall
Then if you don't have one, download a service manual
some here
http://www.forabodiesonly.com/mopar/showthread.php?p=1970088617
and some more here
http://www.mymopar.com/index.php?pid=31
Also at the above MyMopar site are non-factory but somewhat simplified diagrams. These are not always exact, but are sometimes easier to follow
Then go read the MAD electrical article:
http://www.madelectrical.com/electricaltech/amp-gauges.shtml
especially because that article has a simplified basic diagram of the main power
Look at the MAD diagram (from the article):
In the above diagram, follow along. The black wire from the ammeter has a FACTORY WELDED splice a few inches from the ammeter. This splits off and feeds "some stuff" depending on the year. Feeds the fuse box "how" buss, the headlights, and the input to the ignition switch at the very least.
Then it goes back out through the bulkhead connector to the ALTERNATOR
This is the very first thing I'd try----disconnect the alternator output wire (big black) and see if the short goes away
To troubleshoot this, disconnect the battery ground cable, and hook a test lamp from the battery NEG post to ground. When it stops lighting up, you have fixed the short. Don't forget to turn everything off, including the dome and other lights
Ok the very first thing we need to know is "what year make and model" are you working on, because I doubt it's a hemi powered Farmall
Then if you don't have one, download a service manual
some here
http://www.forabodiesonly.com/mopar/showthread.php?p=1970088617
and some more here
http://www.mymopar.com/index.php?pid=31
Also at the above MyMopar site are non-factory but somewhat simplified diagrams. These are not always exact, but are sometimes easier to follow
Then go read the MAD electrical article:
http://www.madelectrical.com/electricaltech/amp-gauges.shtml
especially because that article has a simplified basic diagram of the main power
Look at the MAD diagram (from the article):
In the above diagram, follow along. The black wire from the ammeter has a FACTORY WELDED splice a few inches from the ammeter. This splits off and feeds "some stuff" depending on the year. Feeds the fuse box "how" buss, the headlights, and the input to the ignition switch at the very least.
Then it goes back out through the bulkhead connector to the ALTERNATOR
This is the very first thing I'd try----disconnect the alternator output wire (big black) and see if the short goes away
To troubleshoot this, disconnect the battery ground cable, and hook a test lamp from the battery NEG post to ground. When it stops lighting up, you have fixed the short. Don't forget to turn everything off, including the dome and other lights