12V motorcraft alternator not charging

Went 240 miles to visit my recently aquired 1958 Ford 851 with non-charging alternato. I performed tests with an ANALOG meter as follows: Engine off, ignition off, put the meter leads on the battery and read about 12.1 volt. Then ran engine and still had leads on the battery posts and read 11.9 V. at idling and 11.7 V. at about 1500 rpm(by ear). Apparently not charging. Then with engine still running I placed the meter leads on the alternator connections(Field, Grd, Bat, Sta) in all possible combinations. I do remember that I did not get any kind of reasonable charging voltage but I do not recall if whether I was getting no voltage at all(old age you know). Is this Motorcraft unit similar to the usually mentioned DELCO 10-SI alternator? I need a wiring diagram for this alternator showing where the leads should be wired to. First mistake, I should have brought alternator home for a bench test at the auto parts store. Thanks. Joe in NYC.

For it to charge, you need voltage from the regulator TO the FLD terminal... the more voltage and the FLD terminal, the more it will charge.

To check to see if the alternator itself is working, simply remove the wire from the FLD terminal, and insulate it, and move it out of the way. Jumper full battery voltage to the FLD terminal (full-field it), start the engine, and the alternator should charge at MAX output.

Above is a simple diagram, commonly used in ag and industrial stuff of that era, showing how to wire up the regulator and alternator.

Bob,
There is a voltage regulator with the I, A, S, F leads but it is unplugged. Mine shows the 'I' lead on the plug going to one terminal (block of 2 leads) which goes to one side of the ignition switch and also to one side of a resistor at least 10 WATT(could read resistance but will measure it next time). The 'A' lead goes to the second terminal(of the above block) and from which 3 leads go out, one(black) to the second side of the ignition switch, two(blue) to one side of the ammeter, three(a heavy yellow) I bekieve to the solenoid. The 'S' lead has 2 wires going out but was not able to trace them. The 'F' lead has one wire(green or blue?)but could not trace it out either. My alternator also has 2 ground connections and the 'STA'(stator?) connection. Right now the stator has a BLK wire going someplace(?). On my next trip up I will try FULL FIELD hookup and see if it puts out juice. Thanks for the reply. Joe in NYC.

The diagram I posted is the simplest I've seenm and DOES work.

All the extra wires you have... a guy WITHOUT a diagram tried to transfer over a charging system from a car, complete with a bunch of unneeded wires.

IF you HAVE to have an "idiot light" (NOT shown in the diagram I posted), things get a little more complicated!

Here is picture #2