GM Metro/Sprint 1985-1993 Repair Guide



All models utilize an integral regulator charging system. The integrated circuit (IC) regulator is a solid state unit that is mounted inside the alternator to the rear end frame. All regulator components are enclosed in a solid mold to protect them from the heat and corrosive elements.

The alternator rotor bearings contain enough grease to eliminate the need for periodic lubrication. Two brushes carry current through two slip rings to the field coil, mounted on the rotor. Under normal conditions, this arrangement is capable of providing long periods for attention-free service.

Stator windings are assembled inside a laminated core that forms part of the alternator drive end frame. A rectifier bridge, that contains six diodes, is connected to the stator windings. These diodes electrically change stator AC voltage into DC voltage. The DC voltage is then transmitted to the alternator output terminal.

Two neutral diodes are utilized to smooth out voltage fluctuations caused by varying alternator speeds. A capacitor (condenser), mounted in the regulator, protects the rectifier bridge and neutral diodes. This capacitor also suppresses radio interference noise.


To prevent damage to the on-board computer, alternator and regulator, the following precautionary measures must be taken when working with the electrical system.

Never reverse the battery connections. Always check the battery polarity visually. This is to be done before any connections are made to be sure that all of the connections correspond to the battery ground polarity.
Booster batteries for starting must be connected properly. Make sure that the positive cable of the booster battery is connected to the positive terminal of the battery that is getting the boost. This applies to both negative and ground cables.
Make sure the ignition switch is OFF when connecting or disconnecting any electrical component, especially on trucks equipped with an on-board computer control system.
Disconnect the battery cables before using a fast charger; the charger has a tendency to force current through the diodes in the opposite direction for which they were designed. This burns out the diodes.
Never use a fast charger as a booster for starting the vehicle.
Never disconnect the voltage regulator while the engine is running.
Do not ground the alternator output terminal.
Do not attempt to polarize an alternator.


See Figures 1 and 2

Click image to see an enlarged view

Fig. Fig. 1: Adjusting alternator drive belt tension

  1. Disconnect the negative battery cable.
  3. Remove other components as necessary to gain access to the alternator.
  5. Label and disconnect the alternator's electrical connectors.
  7. Remove the alternator brace bolt and the drive belt.
  9. Support the alternator while removing the mounting bolts, then remove the alternator.

To install:
  1. Install the alternator and loosely tighten the mounting bolts.
  3. Install the drive belt and tension to obtain a deflection of 1 / 4 inch on the longest span of the belt.

Click image to see an enlarged view

Fig. Fig. 2: The alternator is located next to the water pump at the front of the engine

  1. Tighten the alternator drive belt adjuster bolt to 17 ft. lbs.. (23 Nm).
  3. Reconnect the electrical connector and tighten nut to 71 inch lbs.. (8 Nm).
  5. Connect the negative battery cable.