Hello, My 1979 ford is drawing power from the battery through the orange/FLD wire on the alternator. I don't think it is the alternator because I just replaced it hoping to solve this problem, but it just narrowed it to the FLD wire. What do you think is the problem?

thanx, ssg

 

Well, as we say around here "new" does not necessarily fix your problems!

But that said, it sounds like either the voltage regulator is bad, or the Green w/red wire is getting power from somewhere to keep the regulator energized.
Does your regulator connector have three or four wires? Or more accurately, are three or four of the positions filled?

Either way, pull the connector and measure voltage at all the wires. In a 3-wire setup that most of our trucks have (when there is an ammeter in the dash) you should see these readings:

1. Yellow wire(s) should have battery voltage at all times.
2. Green w/red wire should have battery voltage only when the key is in RUN (not in ACC or OFF)
3. The Orange wire should have zero volts at the connector.
4. When the key is off, but the connector installed on the regulator, it sounds like you already know it's got power when off, but triple check with the rest of the wires anyway.
4. Verify that the Orange wire has no power when disconnected. If it does, then it's getting it from somewhere it should not be. Either the alternator or some other short-circuit.

If you have the option, leave the connector disconnected overnight to see if the battery drain persists. If not, then you've narrowed it down and, if it's not any of the wires causing mischief, you will need a new regulator.

Paul

 

A bad diode will make the alternator drain the battery. But the fact that the problem occurs with two different alternators makes me question elsewhere in the charging system.
Have you added anything electrical to the truck recently?