The light bulb will limit current to a safe level, but it can also limit it so much that the circuit doesn't work. If you find the engine never starts with the bulb in place of the fuse, use a larger bulb, like part of a headlight bulb. A tail light bulb will allow about an amp of current to flow when it's feeding a dead short. A brake light will pass about one and a half amps. A typical low beam headlight will pass around five amps. That's usually enough to let circuits work, and the bulb will still just be full brightness when the short occurs.
If you can drive the car that way, and the bulb goes from dim to brighter when the engine stalls, that's the time to leave the ignition switch on and start unplugging things. Don't overlook a wiring harness to an oxygen sensor falling down onto hot exhaust parts and grounding out.
Friday, September 5th, 2014 AT 12:06 AM