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mgf
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Discussion Starter #1 (Edited)
Hi, I have a 2000 mk2 mgf and the fuse for the rear brake lights blew (fuse 16) I replaced the fuse with one of the same rating (15amp) but went out for a drive and the cab filled with smoke and the smell of burning , quickly turned of the engine and let everything cool down, the replaced fuse had been melted not blown but the plastic around it had been melted away, pulled the fuse and drove home without brake lights without any problem, pulled the fuses around, fuse 17 (radio) and 15 (air con) both 10 amp and tied again, same as before the outer casing of fuse 16 melted.
Does anyone have any idea what the hell is happening and an idea to fix it hopefully without replacing the fuse box?? Thank you
 

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First of all fuse should not have melted plastic around as that means fuse did not blow when it should. I suggest to use better vendor of fuses as the ones you used certanly are not good.

Second point to look is in the boot area as there you have possibility of wires which can become bare and touching car body or other bare wires. That would be my first thing to look.
 

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mg_tf
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Adding to Rovrlike’s reply, have you or someone else replaced the radio as it’s quite easy to trap wires between the radio and sharp edges behind the dashboard.
 

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mgf
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Discussion Starter #4
Adding to Rovrlike’s reply, have you or someone else replaced the radio as it’s quite easy to trap wires between the radio and sharp edges behind the dashboard.
The radio is the one that came with the car, it's not the original MGF but has been in the car for a good number of years and looks like it was professionally fitted as it is a "dab" stereo with an aerial on the window
 

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mgf
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Discussion Starter #5
First of all fuse should not have melted plastic around as that means fuse did not blow when it should. I suggest to use better vendor of fuses as the ones you used certanly are not good.

Second point to look is in the boot area as there you have possibility of wires which can become bare and touching car body or other bare wires. That would be my first thing to look.
Will look out today for better fuses and let you know, would the boot wiring still affect the break lights even though the car doesn't have a brake light on the boot ? no 3rd brake light, this all happened the other day, my partner had taken the car and when she got back from work asked me to check the lights and fuse 16 had blown, we have had this car for nearly a year and not had any fuse problems before this, i recently replaced the starter motor and clutch master and slave cylinder could this have something to do with it? the bulbs in the brake lights have not blown as far as i can see,
thank you for your thoughts
 

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Hmmm, without third light boot wires might or might not be a problem. Worth to check wiring to tail lights. Do you have covers for tail lights in the boot, or you can see wires? If you can see wires, maybe something caught them.

Regarding taken work on your car, since working in the engine area, these wires do pass through engine space, so something might caught on them there as well, but this is guessing game...
 

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mg_tf
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Would be worth checking the wiring harness within the flexible section between the body and the boot lid. This can be an area of problems due to the opening and closing of the boot leading to wires breaking and touching one another or earth.
 

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mgf
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Discussion Starter #8
Managed to get to Halfords and got better fuses, so now they blow rather than burn :rolleyes:, checked the wiring on the boot hinge and it looks like there was problems before as all the wires are soldered together but no break or rubbing, all the bulbs in the rear clusters work, partner climbed under the steering wheel (she's slimmer than me lol) to check the brake switch and thinks she found the problem, what do you think and how do i look at repairing it?
 

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What I see in the pictures are melted wires and plastic wrap around wires. That happened at time when you used fuses which did not blow but melted.
I do not think that wires are the original problem. Your original problem might be in the brake pedal switch. Wires damage came later.
My suggestion would be to change brake peadl switch, and separately isolate each wire that has melted isolation around. The best course of action would be to replace melted part of wire, but that depends how good are you with wires.
My warning is that with wires in that situation, you cannot be sure where wires melted further along the line, so best would be to completely replace wires from brake switch to the fusebox.
 

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mgf
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Discussion Starter #10
An update, so I totally stripped out the front of the dash to get to the wiring loom and repaired the wires that were burnt, soldered new wires in and used heat shrink over the joints, got new brake sensor and refitted the connector, rebuilt the dash car started first time so switched it of put new fuse in 16 and turned the key, yep it blew, unplugged the brake sensor and the reversing sensor (which goes by the starter motor so could have been pulled when being replaced) and the fuse still blew!!! So now it's either the fuse box or a wire somewhere, i'm hoping for the fuse box, easier to replace lol.
Any other ideas??
 

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Do you have wiring diagram and connector pinning? With diagram and usage of multimeter you can narrow where the problem is. If fuse blows as soon as you turn the key, then you have permanent contact of power wire to ground, and with use of multimeter, you can narrow where to look.
 

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mgf
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Discussion Starter #12
Hi, yes i have a mgf electrics manual and a multi meter that is "borrowed" at the moment so will chase that up, from what i can see and understand there is 1 wire a permanent live coming from the fuse box to the brake switch this is then daisy-chained to the reversing sensor, another wire comes from the brake switch to the brake lights (switchable live) this would not be a problem because no switch, same with the reversing switch and the switchable live to the reversing lights with the switch not being connected, so thee only wire that could be a problem is the permanent live wire and that is buried in the loom :eek:, have ordered a fuse box hopefully it's a micro burn in the fuse box and that is shortening out the wire, well can live in hope, sorry if this is difficult to follow trying to work it out in my head as i write it down lol
 

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Not a problem, I can follow you. Actually you are not looking for micro burn, you are looking for permanent contact to ground. This contact should be good since you put false fuse and that created so much heat melting plastic. If it is micro contact I would expect it to melt under that heat.
 
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