Hi,

I am being driven demented by an intermittent electrical problem on my 2004 Ford Fiesta.

The IGN fuse regularly blows while I am driving (on average once every three or four days).

I took the car to an auto electrician and he said the IGN fuse on the Fiesta is used to protect more circuits than just the cars ignition. He said according the wiring diagram a problem with the break lights could cause this fuse to blow. He noticed the break\driving light bulb was broken with filaments touching and suggested this might be the problem. The IGN fuse blow again the next day. I've since noticed that the break lights are on a separate fuse (labeled STOP), so the electrician must have been just chancing his arm.

Has anybody here any experience of this sort of problem or any suggestions what I should do next?

 

I would get yourself a wiring diagram, then see exactly what else is on the ignition circuit supply, then if you can disconnect everything so it is all isolated from each other and do resistance tests to earth, as it's most likely a slight short over a period of time doing the fuse in.
Also try to think is it just after you've gone over a bump in the road etc when it blows as this may also give a clue.
tabetha

 

Thanks tabetha, I took your advice and bought myself a haynes manual today to take a look at the wiring diagrams.

It looks like in most of the circuits this ING fuse is simply used to protect the Ignition switch (as you would expect) and is only used for turning on and off the ignition relay.

The typical scenario is

(Battery Positive) ==> (60A Fuse in Engine Bay) ==> (15A IGN Fuse) ==> (Ignition Switch) ==> (Ignition Relay) ==> (Earth on battery negative connector and Earth on Clutch Bell Housing)

Nearly all other circuits have a fuse after the ignition switch .e.g. the lights circuit is

(Battery Positive) ==> (60A Fuse in Engine Bay) ==> (15A IGN Fuse) ==> (Ignition Switch) ==> (10A Fuse for lights) ==> etc

This fuse after the ignition switch would blow before the IGN fuse if there was a problem with the lights for example.

Would it be correct to assume that my problem must be an exposed wire somewhere in first circuit above (i.e. the one involving the relay).

I took a look at the earth connector to the negative connection of the battery and it looked very dirthy.

Would a dodgy earth connection cause a fuse to blow?

 

No dicky earth won't normally cause a fuse to blow, they blow due to passing excess current, I would see about maybe swapping the relay if a common one, and just inspect the wiring as best you can.
tabetha

 

As said earth problem would not make fuse blow, will be caused by excess current or a short in the circuit as you say all circuits have there own dedicated protection. As you say could be esposed wire shorting causing fuse to blow although I would not expect this on new wiring though, check the relay hasen't broken down inside causing the problem.

Martin

 

Thanks tabetha and martysmartie for your help, I found the source of the problem.

A piece of the insulation on the wire going from the ignition relay to the ignition switch had melted away.

It must have been making contact with some hot surface.

I'll try and find where the heat was coming from and isolate it.

I took a picture of the culprit.