Cranks But Won't Start After Reverse Polarity Jump - Blown 7.5A Ignition Fuse

Electricalbeginner✓ OP Confirmed

Problem

1990 Supra Turbo (7M-GTE) cranks but will not start. The issue began after jumper cables were accidentally connected in reverse polarity, which blew the 100A main fuse. After replacing the 100A fuse and installing a new battery, the engine would crank but not fire.

Engine cranks but will not startBattery had been dying quickly prior to incident100A main fuse blew from reverse polarity jumpNo start even with full gas tankNo start with throttle applied during crankingNo start with push/pop start attempt

Root Cause

The reverse polarity jump start blew the 7.5A ignition fuse (in addition to the 100A main fuse). Replacing only the 100A fuse restored cranking power but the blown ignition fuse prevented the ignition system from operating, so the engine would not fire.

Confidence

High confidence — Original poster confirmed this resolved the issue

View Original Thread →Posted March 2023 on SupraForums.com