Three Warning Lights at Idle (Battery, Brake, Lamp) - DOA Replacement Alternator

Electricalbeginner✓ OP Confirmed

Problem

After replacing a failed alternator on a 1990 Supra Turbo, three warning lights (battery, brake, and lamp failure) appeared on the dash. The lights would illuminate at idle and above 2000 RPM, but turn off between 1100-2000 RPM. The alternator was not charging the battery - only 12-12.6V was measured at the battery with the engine running instead of the expected ~14V.

Battery warning light on at idleBrake warning light on at idleLamp failure warning light on at idleWarning lights turn off between 1100-2000 RPM onlyWarning lights blink on/off when engaging clutchAlternator not charging battery - only 12-12.6V at battery with engine runningBattery draining due to lack of charge

Root Cause

The replacement alternator purchased from AutoZone was Dead On Arrival (DOA). Despite passing AutoZone's in-store test, the alternator failed a bench test at NAPA and was not actually charging the battery. Defective rebuilt alternators are a common problem with budget auto parts stores.

Confidence

High confidence — Original poster confirmed this resolved the issue

View Original Thread →Posted May 2021 on SupraForums.com