Article 930 - 55 and 60 Amp Ford Manufactured Alternators - Diode Failures

TSB #49 - November 4, 1966
(All 1966 Models)

Recent evaluations show that Delco diodes contained in rectifier assemblies installed on Ford manufactured 55 and 60 amp alternators are susceptible to excessive reverse current leakage. Approximately 50 percent of Ford manufactured 55 and 60 amp alternators have rectifier assemblies containing Delco diodes. All those rectifier assemblies which contain Delco diodes which you encounter should be removed from the 55 and 60 amp alternators and replaced.

Excessive reverse current leakage on vehicles equipped with an alternator warning light can result in the field relay remaining closed after the engine has been stopped. If the field relay does stay closed, the battery will become discharged because of a continuous current flow through the field circuit. The discharge of the battery will cause the warning light to glow dimly when the ignition key is turned off. Reverse current leakage can be sufficient to cause the field relay to remain closed and still not be sufficient to affect the alternator output noticeably. Consequently, this type of diode condition often cannot be detected by the use of most diode testers or the Rotunda alternator system tester. However, the condition can easily be detected by the following procedure:
  • If the alternator warning light remains on after the ignition key has been turned to "off", disconnect the plug at the field relay or at the alternator regulator assembly and at the same time listen for a click sound. If a click sound is heard, the warning light is staying on because of diode leakage. The click sound is made by the opening field relay which had remained closed. Correct the problem by removing the alternator and replacing its rectifier assembly only.
  • If a click sound is not heard when the plug is disconnected, either the field relay has already opened as it should, or the field relay contacts are stuck. Remove the voltage regulator cover and inspect the field relay contacts. If they are stuck, replace the voltage regulator assembly. If the field relay contacts are not stuck, look for a possible short in the wiring loom which may be causing the warning light to function improperly.

Vehicles equipped with instrument panel ammeter are not affected by this type of diode leakage, except when it is severe enough to affect alternator output in which event it will be easily detected with the Rotunda alternator system tester or with a conventional diode tester. Be sure to allow the alternator to warm before testing, by running the engine for approximately 20 minutes, since reverse current leakage often cannot be detected while the alternator is cold.
The procedure for proper removal and installation of the alternator is outlined in Group 13-13 of the vehicle Shop Manual.

    1. Unsolder three (3) stator lead wires from rectifier circuit board. Use a small soldering iron or gun rated at 100 watts or less. Melt the solder and open the wire loop and then remove the wires from the terminal pins. Excessive heat can damage the circuit board.
    2. Remove the stator terminal screw, the insulating washer and the stator wire terminal. Refer to Illus. S1125-A.
    3. Remove the mounting screw.
    4. Position stator wire terminal under head of the stator terminal as shown and install stator terminal screw and a one-inch diameter insulating washer.
    5. Install mounting screw as shown.
    6. Position stator wire so that no interference to rotor or rear housing will result.
    7. Solder three (3) stator lead wires to rectifier terminals. Polarity is not important but solder each wire to the nearest terminal with the center wire on the center terminal. Maintain a spacing of approximately one-inch between circuit board and stator core. Bend surplus length of stator wires sideways to prevent them from contacting the rear housing.
All 55 and 60 amp Ford manufactured alternators (part numbers C5TZ-10346-C, D, & H) and all rectifier assemblies (part number C5AZ-10304-A) in dealer service stock should be examined to determine if they were assembled with Delco diodes. The Delco diodes can be identified by eight notches on the outer edge of the diode flange. Illus. S1126-A shows notches and how the diodes can be observed through the vent holes in the alternator housing.

Illus. S1125-A
Illus. S1126-A

Oper: 10300A and 10300 A 6
Time: Use appropriate vehicle time