Headlights Always On (1989 Supra with 1JZ Swap) - B1 Connector Pin 22 Ground Issue

Electricalbeginner✓ OP Confirmed

Problem

On a 1989 Supra (with 1JZ swap), the headlights turn on immediately whenever the battery is connected, regardless of headlight switch position. The headlights stay on even when not popped up, and the issue is not related to high beams. Fog lights can still be toggled independently with the headlight switch.

Headlights illuminate immediately when battery is connectedHeadlights stay on regardless of headlight switch positionHeadlights are on even when not popped up (retracted)High beams are not affected (only low beams stay on)Fog lights still function normally via headlight switch

Root Cause

On the 1989 model year specifically, the headlight relay signal wire (pin 22 on the B1 ECU connector) is paired with a wire that goes to ground. On 7M-equipped cars, this connection allowed the ECU to detect headlight operation and raise idle speed for increased alternator output. On 1JZ-swapped cars (where the ECU has no headlight relay input), this ground signal permanently energizes the headlight relay, keeping the headlights on at all times. Other model years route this wire to a non-grounded input (tail light circuit), so they are not affected.

Confidence

High confidence — Original poster confirmed this resolved the issue

View Original Thread →Posted June 2010 on SupraForums.com