What is causing my battery to drain!?

mrtask

mrtask

Well-Known Member
I shelled out for a brand new battery only a few weeks ago. I have noticed that the IGN warning lamp glowed dimly most all of the time. Sometimes it would illuminate brightly. Now and then a stab of the gas pedal would put it out again for a while. Yesterday I stalled halfway reversing into my lock-up garage and trying not to collide with the bicycle my missus had parked precariously and very much in the way! Wouldn't start again. Dead as a Dodo. Schlepped it indoors and hooked up the battery charger. 12.2 V and only one of four bars showing of an icon with five bars when fully charged. Ooof! 14.2 V and four bars by the morning. Car starts on the button again. IGN still glowing faintly now and then though.
The AA guy who helped me with this issue a few months back reckoned I need to run a new wire from the Alternator back to the Ignition Switch. This wire, white and brown, seems to be buried right at the core of the wiring loom under lots of sticky yucky tape! The guy reckoned it is now brittle from half a century of heat cycles in the engine bay and not fit to continue!
I sheepishly admit I didn't buy the multimeter you all told me to acquire last time. Guess I'd better go get one now.
At this point I would very much welcome suggestions for a good Auto Electrician in the North London area who could rectify this issue for me, so do chime in if you know somebody! Failing that, I'll be back for more advice, perhaps armed with a cheap Multimeter, in due course...
 
I would suspect the alternator at first. I’ve found that Lucas alternators of this vintage have a weird failure mode. (See my flatbed of shame ride last spring). They tend to produce power at idle (around low 13v) after about 15-30 minutes of driving that can drop to nothing with no warning light showing. Try measuring voltage at idle when started followed by another measurement after half an hour. It should show around 14.4-14.7v when working correctly.
 
Does sound like alternator, unless there is some badly degraded wiring in there. With a meter, check the volts at the alternator, and then at the battery poles - these should not differ by much - maybe 0.1-0.2v. If the difference is greater - clean all contacts you can - disconnect the battery, clean the poles and the connections with wire wool, grease. While battery is disconnected, pull the connector at the alternator, clean, apply Deoxit or similar , reconnect. Also undo the earth bolt, clean, grease. Good annual practice is locate all earth connections, disconnect, clean, Deoxit, reconnect. while under mine recently I found the connection for the W/Y wire on the solenoid was poor - this shown as feed to the coil while cranking, but as I have a non ballasted coil I dont think its relevant.
I have had a Valeo go bad on me - OK until up to temp, then charge dropped off completely. Tested this by fitting a meter to the cigarette lighter socket, starting it and watching the meter - at around 12mins, volts dropped from14.5 to 12.3, which is just battery.
 
Hi Mr. T,

If your ignition light glows at idle but slowly fades out with increasing engine revs, then the rectifier within the alternator is the problem and will need replacing.

If this is not the case, then leakage current through the voltage regulator will also result in your battery going flat over time. If you disconnect the connector from the back of the alternator, use a multimeter on the current setting, then measure the current being drawn between the two. As the connector is directly connected to the battery, what you are measuring is the current being drawn from the battery. It should be essentially zero if there is no problem.

Ron
 
It could be the alternator.. or old wiring.. but really, buy a decent multimeter and start looking at what the car is doing when you're doing stuff with the car..
 
alternator is number 1 suspect .even 1 diode going bad will allow discharge when stationary. might also account for light /battery not fully charging etc. with a multi meter you can check not just voltages but with care!! check low amperage in a circuit on many meters. thus with everything OFF we can test circuits are if we have a power drain. if we find one pulling an amp(milliamps) os so we will have found our faulty circuit. only an electric clock will pull power with ignition off an thats so small needs a decent meter to register. good luck.
 
You must log in or register to reply here.
Back
Top