15A fuse blows!

Nando559

Registered User
Im working on a 1990 Thunderbird SC Automatic. When I replace the fuse for the interior lamps(under the dash) it blows out right away. I tried adding a 30 amp fuse and everything worked again but fried the fuse box by the next day:p I replaced the fuse box and Im stuck with the same issue again. Any advice on where to start is appreciated. Im a NOOB to electrical issues:rolleyes:

-Fernando
 
Im working on a 1990 Thunderbird SC Automatic. When I replace the fuse for the interior lamps(under the dash) it blows out right away. I tried adding a 30 amp fuse and everything worked again but fried the fuse box by the next day:p I replaced the fuse box and Im stuck with the same issue again. Any advice on where to start is appreciated. Im a NOOB to electrical issues:rolleyes:

-Fernando

Buy a copy of the EVTM for your car, either from eBay or from Helm Inc.

(EVTM - Electrical Vacuum Troubleshooting Manual, Ford # FPS-12116-90 on my copy of the 1990 one, from September 1989.)

But looking at my copy (Section 89), I would say the FIRST thing to check would be the wiring to the underhood lamp - I'd lay even odds, from the boneyards I've been in and from my history on my car, that the wiring has had the insulation fray and it's shorting out the 12V side. Or at least leaking to ground with considerable current.

You MAY spot where the insulation has gotten hot.

BTW - Do not, Do Not, DO NOT, DO NOT UNDER ANY CIRCUMSTANCES do such a boneheaded stunt as swapping in an oversized fuse again, until you KNOW why that fuse is blowing. Unless you just want to burn your car to the ground. That stunt is in the same shape as using a lit match to see how much fuel is in your gas tank by dropping down the fuel filler when it's almost empty. Think "Big BOOM!!!" ...

If you're troubleshooting, you CAN buy circuit breakers (think "Self-resetting fuses") that will plug in where the ATC fuses come out. I used one troubleshooting a short in my A/C compressor clutch line (well, didn't know that was where it was until I troubleshot it ... ) so I wouldn't have to keep buying that 15A fuse. Replaced the breaker with a fuse, and it's still good now that I've replaced the spot where the insulation had gone bad and it was shorting out.

RwP
 
Thanks Ralph for your help.

I guees Ill be taking apart the dash if thats the only way to go about this. Since its not my car, I wont be buying any books for it unless the owner wants to pay for them.

Again, thanks for your help.

-Fernando
 
Lift the carpet near the front of the seat, next to the door (both sides?) to see if any wires are damaged there. I should add that it helps to remove the plastic trim along the bottom of the door opening...two or three screws - there are wire bundles that run along the floor there that you can visually inspect with special tools, diagrams, etc. Sometimes they take a beating under feet - I think the later years had a recall from Ford about it, at one time, on the pass. side, maybe.

As well, remove the bulbs you can reach easy enough that depend on that circuit to see if you can stop the fuse from blowing and help isolate the issue?

I think there are like 10 bulbs at least, not counting the keypad on the door, I think.
 
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this is funny, but I blew this same fuse yesterday. i had been working on my park brake and I had the bulb out of the center console lamp and the harness shorted out! oops.
 
Thanks for the help Ken. I haven't had a chance to work on the SC yet due to crazy weather and work. I will post what I find or dont find when I get to work on it hopefully today. Thanks again for the great suggestions/help.

-Fernando
 
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