hello need some help car wont start no spark checked fuses room fuse blwn and keeps blowing every time i replace any ideas.
What is a room fuse in relation to a car?
Was wonderin the same thing ???
The interior light, as I found when I accidentally shorted it when fitting a new bulb.
I think it may also cover the cigar lighter - do you have anything plugged in there and could it be faulty?
Which model of car is it and how old is it?
A blown room fuse will not stop the roadster from starting???
The FAQs are a wonderful source of all sorts of strange facts, like the answer to “what’s a room fuse?”
The room fuse is the permanent 12v supply (i.e. does not need the key in the ignition) that the interior lights uses.
Also on this circuit is the permanent 12v supply to the stereo to keep the clock and your radio presets stored.
If this is blowing, I’d start with the stereo to make sure this is not earthing somewhere.
To isolate the fault, useful to know if the room fuse blows at the point when you try to start the car.
Also, just a thought, but from experience i would try: (assuming a short has occured)
Disconnect the battery and reconnect.
Give it 20mins or so if you have an immobilser fitted.
See if it will start then.
If not, check the big 80amp or so fuse under the bonnet.
A blown room fuse will stop the car starting as it supplies power to the ECU.
And pray tell where have you heard this Drew???
[quote user=“Mazda-mender”] [quote user=“MX-Drew”]
A blown room fuse will stop the car starting as it supplies power to the ECU.
[/quote]
And pray tell where have you heard this Drew???
[/quote]
The circuit diagram shows a feed to the ecu from the room switch, but I have no idea what it does [bottom left hand corner] 
Hi Geoff
That section of the circuit diagram does not show the “Room Fuse” so it is not possible to interpret what influence the fuse may have on that circuit.
Alan
And pray tell where have you heard this Drew???
[/quote]
The circuit diagram shows a feed to the ecu from the room switch, but I have no idea what it does [bottom left hand corner]
[/quote]
I think by far the easiest way to do this is going to be to pull the room fuse and see if mine starts.<o:p></o:p>
Opps, my eyes are getting a bit old these days, sorry Geoff.
Alan
PS Part of my job used to be checking wiring diagrams, good job I don’t need to rely on that source of income any more!
As a a retired chartered engineer, I should know which way up to hold a cct diag
MX5 Drew “A blown room fuse will stop the car starting as it supplies power to the ECU.”
Well i can safely report Drew that removing the room fuse dose not stop your Mx/ roadster from starting
Where the hell did you hear or read that tosh???
That “tosh” came from Mazda’s circuit diagram, it seemed fair to say cut power to the ECU and the car won’t start.
Oh well more weight saving, throw the ECU out.
Second thoughts, throw Mazda’s circuit diagram out.