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MG MGF Technical - TF Electrical Problems

Hi Everyone

I have a 54 135 TF. A couple of weeks ago when I started up the battery charging light didn't go out until I'd driven half a mile. I drove home (10) miles and tried restarting it to see what the light did. Much to my surprise after a few seconds the light went out before I'd even started the engine. I tried it a couple of more times and the same thing happened.

Next morning the battery was flat. I put it on charge for a couple of days and when I tried it started fine but the ignition light still goes out without the engine being started.

I've tested the alternator using a multimeter across the battery and it is charging. I've disconnected the earth lead from the battery and using the multimeter find that there is 0.5 amp discharge with eveything turned off, even with boot and bonnet bulbs removed.

anyone come across this before? disconnecting the earth lead every night means it starts first touch but I need to find a solution.


John W
J Whiteside


You appear to have 2 probs.

The discharge is too high. You should see 0.04/0.05 at rest with everything off. Rig up the multimeter in series with the live lead and then remove in turn each battery live fuse, hopefully that will pinpoint which circuit is causing the prob. It that fails, disconnect the MFU and the engine ECU, the last F I had a drain problem turned out to be the ECU holding in the MFU!

Had a few instances of trackers lately draining batteries as well. In the last 2 cases the owners didn't even know a tracker was fitted, not having owned the cars from new!

The next thing is to check the charge at the battery, should be 14.5 volts at tickover, dropping slighty with headlights, heater blower running etc. If the alternator fails to charge usually the ABS, SRS ,PAS warning lights come on as they voltage sensitive.

Hope this gives you something to go on.

Regards Steve.

SR Smith 1

The other thing worth checking first is the current drain with the alternator unpluged, since the charge light was acting in a strange way it may be the voltage reg in the alternator drawing the 0.5 amp.
G Luxon

This thread was discussed between 11/05/2011 and 13/05/2011

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