Farmall 400 not charging

make sure the starter and soliniod are not drawing power when the key is on

Duanes - If your 400 has have a Delco internally-regulated alternator procede as below. (Otherwise just disregard....!)

1 - Take voltage readings at the following points (all voltages measured to ground):

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The large post ("BAT") terminal - should read battery voltage.

Now pull the auxiliary wiring connector from the alternator and take readings at the connector. With the ign switch "off" you should see 0 volts at #1 and battery voltage at #2.

With the ignition switch "on" you should see battery voltage at BOTH terminals.

If you don't get the above results the alt is wired wrong, or there's an open diode (or blown indicator lamp if equipped) in the #1 circuit.

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2 - If wiring checks out OK, next test the alternator:

Start and run the engine at about 1/2 throttle. Now with an assistant observing the ammeter, find the "D" shaped hole in the back of the alt (photo above...), take a small screwdriver poke it into the hole until it touches the metal test tab inside then ground the side of the screwdriver against the metal case. If the ammeter indicates full charge with the test tab grounded, the internal regulator is bad and needs to be replaced. However if there's still no charge the alternator is N.G. - time for a replacement!

Hope this helps...

The first effort is to find the reason the battery goes dead in 1/2 hour. If it is charged up with an external battery charger, the battery should keep it running for a week if the lights are not used. This points to a bad abttery, or insufficient chatging of the battery befor starting it. Remove one terminal from the battery post, and charge the battery slowly (8 to 10 hours on slow charge, or with a trickle charger (2 amps). The attached diagram should help. The diode is 3 amp 1000piv radioshack. JimN
Then take a light bulb (1156) and connect the center contact with the battery post, and the side base to the battery cable (putting the filiment in series with the system. If the switch is off, and the lights are off, the bulb should not light up at all (even dim). if it does, there is a substantial drain, and it might be the diode set internal to the alternator. Have the alternator checked at a Auto store.
If it does not light, reconnect the battery. Use an analog (needle and scale type) meter to check battery volts. (put the leads directly onto the posts of the battery). With the tractor shut off the voltage should be about 12.6 volts.
Start the tractor. with it running the voltage with a fully charged battery should be 14.2 to 14.7 volts. If it still reads battery volts (about mid 12s), it is not charging.
On the alternator, the number 2 small terminal should be connected to the big terminal on the alternator. the #1 terminal can temporarily be connected to the battery positive terminal with a jumper. If it now reads 14.2 to 14.7 volts, the problem is in the exciting circuit that you said had the appearance of a light or diode.