GM alternator wiring

GM alternator wiring

GM has many different alternators and each has its own alternator wiring diagram and alternator symptoms. One of the key differences is how the internal voltage regulator determines charge rate. Does it check the vehicle’s voltage internally or from an outside source?

The PDF shown here is for a GM CS 130 and CS 144 alternator. Both of these alternators (generators) can be wired differently depending on their application. They can have a BAT wire and two additional wires, or a BAT and a single “L” wire.

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BAT plus 2

In the BAT plug two wire version, the alternator checks system voltage via a “sense” fuse located in a vehicle fuse box. The whole purpose is to check voltage away from the alternator itself. The reason is pretty simple; it wants to know if the charging voltage is reaching the fuse box. It’s literally checking the condition of all the connections. If the regulator determines the vehicle needs charging based on the input from the sense fuse,
the internal regulator pulses “field” current to the rotor at a fixed frequency of 400 cycles per second. To regulate how much power it generates, it varies the on versus off time of each cycle. At high vehicle speeds with low electrical loads, the on time may be as little at 10%. However, at lower speeds or high loads, the on time may be as much as 90%.

If the “sense” fuse blows or there’s any fault in the connection between the sense fuse and the alternator, the unit sends a signal to the PCM over the LAMP L-terminal. The PCM then provides ground to the ALT indicator light in the instrument panel.

BAT plus 1

This system operates just like the system above, except that it doesn’t sense vehicle voltage externally. So it only has an output to battery (BAT) wire, and a LAMP (L) wire to tell the PCM to light the ALT light. In this setup, the regulator always reads internal voltage to determine charging rate.

© 2012 Rick Muscoplat

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