by Herb Bridge
This note is for older Alfas (about 1968 to 1981). These cars have an external alternator voltage regulator usually mounted on the inner fender, or on the firewall.
So the light stays on. First of all make sure the alternator drive belt is tight and really driving the alternator. If the belt is OK there is a fairly simple test to see whether the fault is in the alternator or regulator. Note that there are three thin wires which connect the regulator and alternator; these terminate in a three prong connector which plugs into the regulator. Usually the color code is green, brown, and black. The green wire goes to the alternator terminal D+ (the output of the alternator exciter diodes); the brown wire goes to the terminal DF on the alternator (this is the input to the rotating field), and the black wire goes to the ground. There is also a heavy red wire which connects from the alternator to the starter solenoid and from there to the battery (+). The green wire also goes to +12 volts through the alternator warning light. This is a three-watt bulb which supplies the initial excitation for the alternator.
When the car is started, terminal D+ is connected to terminal DF inside the regulator. This means that the alternator field is connected to +12 through the three-watt warning lamp: the current to light the lamp flows through the field winding to ground and provides the initial excitation for the alternator. As output voltage rises, it flows through the exciter diodes and appears on terminal D+. The voltage is then equal on both sides of the warning lamp and it goes out.
To determine whether the alternator or the regulator is at fault, disconnect the three prong connector at the regulator; connect the DF (brown wire) terminal in the connector to the D+ (green wire) terminal using a clip lead or a jumper. Start the car and run it at about 1300 rpm--do not exceed 2000 rpm. The warning light should go out almost at once and the battery voltage should increase by about 1.3 volts -- say from 12.6v to 14.1v. If this happens, the alternator is OK, but the regulator is shot. On the other hand, if the light stays lit and the battery voltage doesn't rise the problem is the alternator.
At least one other test on the alternator can be made without taking things apart. Using an ohmmeter with a good low resistance scale, measure the resistance of the brown wire (DF) to ground. This measures the resistance of the field and should be between three and four ohms, depending on the alternator. If the reading is high, the brushes are probably bad and the alternator will have to be taken apart to replace them.
Finally, a rough test of the exciter diode can be made by first disconnecting the green wire which goes to the warning light and measuring the resistance between the green wire in the connector and ground. when the positive terminal of the ohmmeter is connected to the green wire and the negative to ground, the meter should read high -- at least several thousand ohms; when the polarity is reversed, the resistance should be less than a hundred ohms. This test will not tell you if one of the exciter diodes is open; it will tell you if one or more are shorted.
A new solid state regulator that replaces the old electromechanical unit directly is available from Fred DiMatteo or Alfa Ricambi.
by Rex Brown
Beginning in January 1981, Alfa started equipping all US-bound cars with the new Bosch internally-regulated alternators. These "two-wire" alternators not only tidy up the engine compartment, they offer longer life and more serviceability. The voltage regulator is mounted on the rear of the alternator with two screws, period. No wires, no rivets, no glue; just two screws and presto! But the bello vero is what you find on the other end of the regulators once you've removed those screws: the brushes. The regulator and brush holder are a one-piece unit, easy (and cheap) to replace or diagnose.
When replacing these regulators, simply point the brushes into the opening on the back of the alternator and rotate the regulator upward. The brushes on a new regulator protrude about 11 mm past the brush holder when new. If your old brushes are only 60% of that or less you're due for replacement. Also, note the small tang that points forward just to the left of the brush holder. This is the grounding tang. Before installing the new unit, always inspect the spring-loaded tang that this grounding tang bumps up against. The brushes produce dust as they wear, and this tang can get covered with this dust and foul the connection. A "red-rag" with carb cleaner will wipe it right off.
Many Alfisti have changed earlier cars over to these internally-regulated 55 amp alternators since it is so simple. All you need is a foot of wire and two crimp-on terminals to extend the "charge" lamp lead so it will reach the alternator. Depending on which model you're converting, you may (or may not) be able to use your original pulley and fan from the old alternator. The external regulator is a three-wire unit. The green wire is for the "charge" lamp and has a connection about three inches from the regulators. Just unplug this connection and attach your extension to the blade terminal on the new alternator. The big wire goes on the 6 mm stud just like before.
Those of you who still don't seem to have enough juice to run your boombox, AC, microwave, etc., may need to contact Fred DiMatteo, He makes an adjustable voltage regulator for these Bosch alternators. -Ciao