Starter/Alternator fuse blows instantly?

ABELAMAYA44

MEMBER
2002 MERCURY GRAND MARQUIS
4.6L
V8
2WD
AUTOMATIC
230,000 MILES

My car has a 30-amp fuse for the starter/alternator and every time I try to replace the fuse, it blows the moment it makes contact with its slot. All other fuses are good. I checked the battery, starter solenoid and alternator to make sure everything was properly connected with no damaged wires, and I couldn't find anything out of the ordinary. I assume it has a short somewhere. Has anybody come across this? Any suggestions?

Thursday, August 31st, 2023 AT 2:38 PM

1 Reply

JACOBANDNICKOLAS

MECHANIC
110,108 POSTS

Hi,

We need to narrow things down. Fuse 2 (30 amp) in the junction box is for the starter circuit. I need you to remove the starter relay first to see if the fuse still fails.

Power from the fuse goes directly to the relay and ignition switch. By removing the relay, we should know if the short is before or after the relay. I suspect it is before, but this will let us know. Also, the relay itself may have failed or there could be a short to the ignition switch.

If the fuse still fails when you remove the relay, next we will need to disconnect the ignition switch and check if that prevents it from failing.

Let me know what you find when you do this. Note: When you remove the starter relay, shake it to see if anything sounds loose inside it.

Take care,

joe

See pics below.

Images (Click to make bigger)