My 95 Bronco (Eddie Bauer, 302, auto) had a small electrical fire today. I'll go through the whole story so you can better get a feel for what might have happened:
I started up the truck and let the idle lower, then went to shift into gear. However, the shifter wouldn't move, no matter how hard I pressed on the brake or didn't press on the brake. I figured it was an electrical sensor keeping the shifter from moving, so first my bro and I checked the sensor under the pedal, not the problem. Then we checked the fuses, and sure enough, #13, which says it's for "Shift interlock" was blown. It's a 15A fuse. So, we get a spare 15A fuse of the same style and size and put that in. Immediately that one blows. So, we turn off the truck, put in a 20A fuse just to see if that works, that one blows. Now, by this time I need to get going, so he sticks in a 30A fuse with the truck off and immediately smoke starts pouring from under the hood. I pop the hood to see the wire and connector sticking out of the front of the master cylinder smoking real bad. It starts on fire, we put it out and yank it off, but not before that whole electrical piece melts to crap. The plastic master cylinder managed to survive. All right, now that that's disconnected we check to see if any other fuses are blown, but they're all okay. We tentatively start up the truck, it starts fine, shifts into gear fine, no brake fluid loss noticeable. However, I'm worried about what the wire and connector do. I've heard they are involved in the ABS, even cruise control. The cruise hasn't worked for about six months, and I had cleaned that connector with electrical contact cleaner, which shouldn't have led to this fire. Was it the 30A fuse that allowed too much current? Is that even the fuse for that module? Anyone have any ideas on fixing this? The burnt part left on the master cylinder looks like it will just unscrew, so if I can get the wires and connectors from a Ford dealer I should be all set, but is there more to it than that? It drove fine, no noticeable difference in brake pedal feel, although it looked like a little fluid was leaking through the burnt mess, but not much. Probably need to have it bled. Any suggestions?

 

Make a note to yourself: "Don't increase fuse size when it keeps blowing. It is fused a certain size for a reason."

You can usually tell what size fuse belongs where by looking at the fuse block cover.

Overfusing an electrical component, as you have experienced, doesn't solve the problem. While in some cases the component may function, if a fuse is blowing, then there is a problem somewhere on that circuit. The best way to troubleshoot something like this is to start at the end of the line with each individual component on the circuit and work your way back to the fuse. Hopefully, it's a component problem, which would be much easier to locate than a bad wire. Try tracing individual wires through huge wiring harnesses. Not a fun thing to do. In this case, it was probably a grounded circuit at the component, since it caught on fire.

Can't offer more than electrical theory to you. Hope that helps.

 

I second that emotion! What you should have done is to see what was on that fuse, and trace it back. In your case, you could have disconnected that connector, your truck would still have run fine and you could have gotten going, and then fixed the problem later. But at least you didn't put a bullet in the fuse holder. I once read about a guy who replaced a glass-type fuse in his truck with a .22 caliber bullet. Of course, the bullet heated up and eventually shot the guy. DUH!

 

All right, besides my idiocy in putting in the larger amp fuse, can anyone tell me what that sensor on the end of the master cylinder does? Is it cheap to replace? Would it be easy to go to a Ford dealer and just buy the wiring and connector and put a new one in, or am I looking at a few hundred bucks in repairs? Besides, what would cause that fuse to keep blowing like that.

PS - electrical work is definitely not my strong point. I finally got a multimeter for Christmas, but have no idea what the hell I'm supposed to do with it. That, and all this work will have to be done in my campus parking lot in between classes and stuff.

 

I'm not sure what the sensor on the master cylinder does, but I am guessing that it is probably the sensor for low brake fluid that would make your brake light come on if the fluid was low. If this is true, you could certainly live without it. As far as the multimeter, you would basically be using two functions of it for your Bronco. You would use the ohms to test a circuit for continuity, in other words you could do something like place it at two different points on a wire to see if there is a break in the wire. If the ohms does not register, there is a break somewhere between where you put the contacts. Similarly, you can test between points on a board. It is also useful for testing a wire that goes in somewhere, disappears, and then comes out somewhere else. You can use the ohmmeter to see if it is the same wire at both ends. The guage will show one of two readings for ohms: nothing, or all the way. All the way would mean a good circuit, nothing means a break. Note: use the ohmmeter when the circuit is NOT powered up. The second function you will use for your truck is voltage. The proper setting is whatever is the next one up from 12v DC. It might be 120, but make sure it is DC. The reason you don't want to use the 12V setting, even though the truck is 12V, is because you can actually get more than 12V out of the truck, and it would peg the guage and possibly break it. Also, if you want an accurate reading, and your truck is putting out 13V, you wouldn't be able to tell on the 12V setting. You would most likely use the voltage setting either to test your charging system, test a sensor or something for proper voltage, or like a test light to see if you are getting current somewhere.

 

[updated:LAST EDITED ON 30-Jan-02 AT 06:53 PM (EST)]>My 95 Bronco (Eddie Bauer, 302, auto) had a small electrical
>the brake. I figured it was an electrical sensor keeping
>the shifter from moving, so first my bro and I checked the
>sensor under the pedal, not the problem. Then we checked
>the fuses, and sure enough, #13, which says it's for "Shift
>interlock" was blown. It's a 15A fuse. So, we get a spare
#13 is located on the TOP Center of the fuse box.

I see in the schematic that I have that #13 fuse position is for the Brake Light switch,Speed Control,Stop Sensor for Anti-lock brakes.

And is also attached to Fuse #9 which goes to the Aux. Power socket.
Check the condition of fuse #9.

Right now ,I'd say there was a short in the brake light switch,which should be attached to the master cyl.

Dennis

Please Don't Ask Me Any Tough Questions As:
"I'm Saving My Memory For When I Develop Alzheimer's"


78 F-150 429CJ,Silver
w/Explorer Pkge.
641/2-Mustang 260,Pre-World's Fair Car.
64-Fairlane500 S/C waiting for a 390-4spd.
68-Mustang 289-Sunlit Gold 80,892Mi
78-Buick LeSabre 403 4V
84 Volvo DL Wagon

 

 

Fuse 9 comes off power side of fuse 13, so it would not affect 13. Also, connector should not be fluid level. Check your new post for my ideas.

Brad