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Matt Carey
Matt Carey, Mecury Mechanic
Category: Mercury
Satisfied Customers: 258
Experience:  6yrs experience, and access to factory service information
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Mercury: keeps blowing..idle.....the next day drove mile

Customer Question

My mercury problem turn out to be fuse 10 keeps blowing when the car is being driven.....I let the car idle for over a hour then ...the next day drove it less than one mile and it blow the fuse again......I repeated this the next day and it did the same
Submitted: 8 years ago.
Category: Mercury
Expert:  Matt Carey replied 8 years ago.
Okay, Is this Fuse 10 (20 amp) in the power dist. center (under hood)? It is for the Ignition, starting, and head light sw. And you say that it will still blow with the head light sw. unplugged? (but only when the car is warmed up) . let me know, and I'll try to help. MATT
Customer: replied 8 years ago.

Yes its the above mentioned fuse(20amp)....and yes it only blows it when the car is or has been driven, I have run the car stationary for one hour with no problems.

But if i drive it for half a mile it will blow the fuse and will blow any fuses you put in until the engine is cold again..

Thjanks Matt



Expert:  Matt Carey replied 8 years ago.

Just to be sure, you did say that it still blows with the head light sw. unplugged? Correct. MATT


That fuse (F10) , is the power source for the Igniton switch. Then the Ignition sw. sends power on to other components. For example the radio and the inst. cluster. You could start by unplugging the radio, It could be the problem. This will at least rule it out. I'll post some diagrams that will help you.

The problem could be the ignition sw. itself. It's tuff when it doesn't blow everytime. You'll need to test for the short during that window when the car is hot.

One method I like to use when looking for a short is to use a sealed beam head light. Like from an older pick up truck, etc. Connect jumper wires to the light, and then in place of the fuse that blows, connect the wires. So use some crimp on terminals from radio shack, etc. that plug in like the fuse would. In other words, you have the light connected in place of the fuse. Power will flow thru the light, until the short to ground happens. When this happens the light will light up, instead of blowing the fuse. This saves fuses, and you can place the light where you can see it. Start unplugging things that are on that circuit, or wiggling wires. When you find the problem (when you remove the short) the light will go out.

So if you unplug the radio and the light goes out, you know the radio is the problem. If you wiggle the wires at the column to the ignition sw. and the light goes out, then you need to look closer and find the shorted wiring. Hope this makes sense.

here's the diagrams showing what's on that circuit. Let me know if you need anything else, happy to help. MATTgraphicgraphic

Customer: replied 8 years ago.

yes i did disconnect the lights at the switch..

The radio works without the ignition and even when the fuse is blown

will the test light work with a normal healight bulb?

I will try some of the things on the curcuits and let you know

Expert:  Matt Carey replied 8 years ago.

Okay, there are two power sources to the radio, usually one is for memory, and the other is for switched power. The switched power would be the one coming from that fuse thru the ign. sw. to the radio. It would still be good to unplug it to rule it out.

As for the tester head lt. I mentioned, I don't know about a regular head lt. bulb. It all depends on the amp draw of the bulb. It needs to be able to handle the draw of the circuit. A sealed beam head lt is around 5 -7 amps I think?? You could try another bulb, but a sealed beam is not that expensive, and I would have to test some newer head lt. bulbs for amperage to see if they would work. Maybe I can check that at work tomorrow. What bulbs do you have 9004,9005, 9006, etc...

let me know MATT

Customer: replied 8 years ago.
i have a big draw of bulbs........assorted types
Expert:  Matt Carey replied 8 years ago.
Okay, you could try one! If you can wait, tomorrow I can try some and see what I get. I have just always used a sealed beam, so I don't know if newer bulbs will work. I would like to think that if you use a bulb that can not handle enough amps, it would just blow the bulb. But I would hate for you to cause more damage, by melting something, if the bulb couldn't absorb the amps. MATT
Customer: replied 8 years ago.

i wont be working on it until about 2pm et tomorrow so i can wait.

Its strange that the car can run for over a hour, but doesnt last more than a mile when being driven, could it be in the steering colum , cruse control or something



Expert:  Matt Carey replied 8 years ago.

yes it is a tough one, I've been trying to think what would change after driving for a while. I am hoping that you will have a window of time, when the fuse blows (when warm) that you can use to test. Get it warm, then with the tester head light in place of the fuse, start unplugging things and wiggling wires.

Maybe it is in the column wiring, and driving (and turning the wheel) is causing the short. MATT I'll be on line again tomorrow after work, 5pm eastern. MATT

Customer: replied 8 years ago.

thanks matt



Expert:  Matt Carey replied 8 years ago.
Hey, i did some research on line, and it looks like any headlight bulb will work. I looked at the amps rating for different bulbs, 9003 , 9004, 9005. Using the high beam filament should work. talk to you tomorrow. MATT good night