5 replies to this topic

[biscuit90210]

hi i need help trying to work this one out, allready had a look on other pages but no joy as yet!!
just bought my mini 1275 on a 93 plate and had a problem with the battery light coming on every now and then, put a voltmeter across the battery when running and got 12.6, with lights and stereo on i only got 12.1v. Right, secondhand alternator put on which was tested and worked fine?????? great problem solved i thought as the battery light stayed off. But not the case as i found out driving on the m5 in the dark when my lights faded down to almost nothing. luckily i still had the old battery in the boot after fitting a new one at the same time as the alternator. so battery swap on the hard shoulder later, fine lights again but that went flat as well.. looking at other pages on this topic i`ve checked the light on the dash and swapped the bulb so i know the bulb is fine and the engine starts with a charged battery. when i fitted the alternator the connectors in the plug looked a bit grubby so i put new connectors on each wire and connected them to the alt so i know connections are fine.. but i also have no dash lights come on when i turn the ignition on????

please help!!

[Dan]

Check that ignition power is making it through the instrument panel PCB to the no charge lamp socket. Also check that the lamp is making good contact with the socket. If that lamp isn't getting 12v from the battery then even if the bulb is intact the alternator isn't getting what it needs in order to power up.

[jimmyH]

I had this exact problem with my 97 MPI.
A fully charged battery would start it, but eventually run flat not being charged.

The engine earth strap was my problem, i fixed it and it worked for a while then started to give me trouble, so i have a second bulky one fitted and dont have the problem at all anymore.

That would be my first check, cheap to change, i have an old one of a Landy as it was fully sealed and wouldnt rust.

[bmcecosse]

Your old alternator was doing something if it managed 12.6 volts - I suggest the fan belt may not have been tight enough? What volts do you get with the 'new' alternator fitted. Also check you fitted the battery right way round - with the -ve terminal connected to earth......

[Trick77]

When the alternator is working you should be expecting around 14 volts. I suggest the bracket for the alternator is loose. It can sit the alternator in the right position when starting so you get the 14volts and the dash light goes off but then you drive and bump the alternator down so that the fan belt is loose and no charging occurs. The belt should be pretty tight so that it only twists about 90degrees at the longest section. Tighten this and then check the voltage. Hopefully well over 13volts should come through.

[biscuit90210]

Problem solved!!! It was the fact that there was a White wire which comes from the circuit board on the battery light was broken!! Just as it comes from the engine bay through the bulk head. Reconnected and now have batt light on with ignition and then starts and when reved up light goes out!! Now reading 13.8v across the battery when running but it I'd flat at the moment! With a full charge tonight hopeing all is ok tomorrow!!