Electrical Repair: How To Diagnose & Repair Your Charging System Part 3

In part 2 of this series, we discussed the alternator and two possible types of regulator systems, along with some troubleshooting techniques. In this final part, we’ll cover testing for both types of regulator, alternator/regulator replacement, and testing of the associated wiring.

Important: One or both battery cables must be disconnected before replacing any parts.

1) Seperate Voltage Regulator:

If your vehicle does use this type of regulator, then the next step is to locate said regulator within the vehicle and make sure that all electrical connections to the regulator are clean and tight.

Generally speaking, seperate voltage regulators are usually mounted on one of the inner fenders underneath the hood, or on the firewall. A few vehicles integrate the voltage regulator inside the Engine Control Module, but that type is beyond the scope of this article. If you have a service manual for your vehicle as discussed in part 2, it will usually have information about locating and testing the regulator.

If you don’t yet have the  service manual,  then use the following general guidelines:

If you have located the regulator and determined that electrical connections to it are clean and tight and that the regulator is securely mounted & grounded to the vehicle body, then there is little else you can do to test the regulator itself. Excepting some very old types, these regulators are usually sealed, solid-state devices and cannot be repaired.

At this point, you will need to perform a test of the alternator which is called a Full-Field test. In effect, the Full-Field test temporarily bypasses the regulator, thereby isolating the problem to either the regulator or the alternator.

Your  service manual will usually provide details on how to do the full-field test on your particular alternator yourself, or you can have it done at an auto repair shop or dealer. Some auto parts stores can also perform the test.

If your alternator passes the full-field test, then it is highly likely that the regulator is defective and should be replaced. If not, then repair or replace the alternator. Replacing the regulator is usually a simple job; unhook the electrical connections from the old unit, remove any mounting bolts or screws, and remove it from the vehicle. Install the new unit by reversing these procedures.

2) Alternator with voltage regulator built-in:

This type of charging system has just one major component, the alternator itself and associated wiring. The full-field alternator test discussed above can also be performed on this type of alternator, but what to do after the results are obtained will be different. If this type of alternator passes that test, and the tests mentioned earlier in this series have been performed in order to make sure that the charging system output is indeed connected to the battery, then replace the alternator or have it replaced. Nearly all alternators can also be repaired rather than replaced, but that is outside the scope of this article.

Thank you for reading, and I hope that the information presented here will be useful and help you to make informed decisions regarding repairs on your vehicle.