I've isolated the ground fault to the harness that connects under the driver's kick panel (hood release knob). The harness goes to the rear through some cable molding. This harness is dead shorted on the green/yellow stripe wire. I've checked the trunk light cable and receptacle: all OK. I'd be happy to drive the car with this harness disconnected except that the volts for the fuel pump are delivered by the offending harness.
Fuse 8 blows on 1990 Ford Crown Victoria
by WildB in Chelmsford, MA on November 04, 2009
1 answer 6 comments
ANSWER by Bret Bodas on November 04, 2009
I'm not sure what info your looking for, you sound like your very qualified to diagnose and repair this problem. Are you having a hard time locating the exact location of the short?
COMMENT by WildB on November 04, 2009
Thanks for the compliment. The harness is 14A549 if I read the shop manual correctly. The ground fault is on the green/yellow stripe and the black/blue stripe wires. Further testing indicates that the fault is not in the harness since fuse 8 blows with the harness disconnected. I could live without courtesy lights, but #8 also has the motors for the rear view mirrors. Any ideas to help me loctae the source of the grounfd fault?
Unfortunately I don't have the wiring diagram for this vehicle, so it's hard to follow along, but I'll try. If you disconnect part of the circuit and the fuse blows, then the short circuit is between the disconnected connector and the fuse. Can you trace that wire back to the fuse box?
The ground fault appears to be on the black/blue stripe wire, which is fed by the green/yellow stripe wire. Actually, I'm now convinced the car is haunted. Last night, I removed the dome light for the n'th time and fiddled with the black/blue stripe wire up there. Then I slammed some doors and tried unsuccessfully to get the light bulb out of the glove box (try this if you have an old Crown Vic at your disposal: very frustrating). I took a resistance reading on the load side of the fuse: 1+ Ohm. Interesting: if I = E/R, then the draw on the fuse would be a little under 12 Amperes, a presumably comfortable load for a 15A fuse. Before my voodoo ritual, the load side read 0 Ohms. I inserted a new fuse, and all looks well at the moment. Anyone got a wiring diagram for this car? It looks like a fault on the black/blue stripe wire caused by some intermittent failure of a connection to a device like a lamp socket or vanity mirror, or a pinch in the insulation outside of any wiring harness.
If the fuse also supplies the electric motors for the rear view mirrors, then I would look at the wire harnesses where they connect to the door, in between the body and the door. This is where you will find shorts and broken wires, because the wires are moving every time you open and close a door. You can possibly get a wiring diagram from autozone in their free repair manual section, or go to alldatadiy.com, for $25.00 you can get the entire manual online.
Thanks for the guidance and the leads on wiring diagrams, Bret. I'll keep you posted. Bill
COMMENT by WildB on November 29, 2009
All is now well electrically. I never found the source of the ground fault on the green/yellow stripe wire. The harness running to the trunk turned out to be OK. I replaced the dome light fixture with the fixture from my old CV. I did replace all the light bulbs since the map lights had been burned out for some time. The dome light and the other courtesy lights are on the black/blue stripe wire, which seems to be fed by the green/yellow stripe. My guess: the actual dome light bulb (an interesting cylindrical gadget) may have been shorting. Anyhow, Bret, thanks for you help with all this. You gave me some good ideas when I had absolutely none.