Mysterious power consumption on my non VVC, 1999 MGF

Hi everyone. I recently broke down with a faulty alternator (it was no longer supplying enough voltage, but the charge indicator light didn't come on either) when the battery was finally drained. I have now removed the alternator for repair (and insulated the cables of course). So I suppose the power drain is not related to the alternator .

Although I had only fully recharged the battery 4 days ago, it was already flat again. A measurement showed that 1.6 amps (!!) of current was flowing with the ignition switched off and all the entrance lights, etc. were off (battery disconnected and measured between the negative terminal and earth).
Then I pulled the circled fuse (probably ‘Brake Light, Horn’) and the current consumption went down to an acceptable 10mA. Can anyone reveal to me what could be wrong? I have no idea what is causing the power consumption, but maybe this is not an uncommon problem with the MGF.
TIA
Marcus

 

A buggered alternator can drain a battery pretty quickly.
As can other things.
A common culprit in drawing current is the idiotic Lucas 5AS alarm system… a source of never ending problems,
as for that fuse I would need to study the wiring diagram to see what exactly is on that circuit, but alas my manuals are inaccessible at the moment.
However the fuse circled is yellow which is 20 amps, that circuit shoud be protected by a blue 15 amp fuse….what happens when a 15 amp fuse is used? If it blows or melts down slowly then that indicates a problem with something on that circuit.
The brake light switches on these things can be trouble, make sure it’s operating correctly, also check the wiring to the boot lid it can give trouble around the boot hinge, you may have a bit of a short circuit there.
Also as the inside of the boot provides buggerall protection to the tail lights check the isn’t a problem there,
this last one can be easily fixed for all time by fitting tail light guards which were fitted to later cars by MG, and can probably still be purchased from the usual suspects.

I’ve just looked at this & I’ll have a glance at the circuit diagram when I’m in the workshop. However if the circled fuse circuit has brake lights on it & the brake switch is suspect, remaining on or is intermittent, you may not have notice, especially if the car is outside & you’ve not been around the back.
Now that would flatten the battery.
M

Sorry Cobb’s, I didn’t fully read your response, which of course made mine superfluous.
One thing it did turn up though is the disparity between the under bonnet fuse box & the electrical diagram. It would only irritate folk such as me so isn’t worthy of attention.
Our problem car seems to a left hooker & was wandering what the clear plastic fuse holder is protecting. Also the truncated pyramidical box; is that for one shot windows? That usually lives behind the carpet in the right hand footwell.
M

Hi Folks,

thanks for all your valuable tips, which I thoroughly have gone through and what shall I say - I finally found the fault.
It was a PICNIC* case.

Turned out I hadn't fully shut the drivers door, which was more or less jammed against the garage wall. Such I didn't see it being lightly open.
Lesson learnt: The courtesy light draws 1.6Amps
So, now everyone may laugh heartily at me

*Problem in carmechanic, not in car

No more than a smirk at the found misfortune but glad it was a simple problem to resolve & I do like PICNIC acronym.
M

Easily done.