Avoiding Common Installation Mistakes: Alternators

Replacement alternators rarely fail as a result of manufacturing defects, but often quit because the root cause of the original failure wasn’t addressed.

Load testing with a resistive load such as a carbon pile will determine if the alternator can deliver it’s rated current, but it won’t address the original cause of the failure. Diode-killing voltage transients can best be traced with a ‘scope or a good memory multimeter and experience. Dedicated charging system testers also help, but in general, diagnosis takes time.

Compare the replacement unit with the original carefully, since similar looking alternators may differ slightly in the indexing of the rear cover or in mounting bracket details.

An otherwise perfect fit that stretches the wiring or stresses connectors is a failure waiting to happen as the engine floats in its mounts. Wiring and grounds are must-check items, as is pulley alignment and belt condition. Belt tensioners should not only be in good shape, but must operate within the range of the unit’s indicator.

If it’s in good shape, but the pointer falls out of range, then the belt is the wrong size. If a new belt is installed, don’t forget to clean the rubber buildup from all pulleys to prevent slip and squeal.

The battery is always at issue, and in cold weather, when the electrolyte stratifies, should be charged over sufficient time to allow thorough mixing.

And don’t forget to replace the air ducting and check the fan clutch, if necessary. Like most living things, the new alternator needs air to survive.