dim headlights

[eltel]

hi there...

my 1988 325 has of late been suffering with dimmer than usual headlights..the main beam is fine.

both bulbs have been replaced but are the same.

i know that the alternator is only kicking out about 12.5 volts which is a bit low but the mains should also be affected should'nt they???

[Brianmoooore]

Unclip the back cover on the headlamps and measure the voltage 1/ directly across the wires to the bulb, and 2/ from the wire to the bulb centre lead to battery negative (or good body earth).
Haven't fitted 24V bulbs, have you?

[eltel]

no just normal bulbs fitted... if earth is ok and bulb gets less than 12.5 v then its prob the alternator isnt it...thanks for the help

[Brianmoooore]

Alternator needs to putting out about 14 volts or so. Check for any voltage between the alternator alloy case and the battery negative. Corrosion can build up in the alternator mountings.
I've seen more than one perfectly good alternator thrown away because of this, and of course, a new alternator always cures the problem, because fitting it sorts the corrosion.

[kam-325i]

Mmm....

Ok...im having a thick moment.....should there be any voltage between alternator casing and battery - ?

[Brianmoooore]

Mmm....

Ok...im having a thick moment.....should there be any voltage between alternator casing and battery - ?

No, shouldn't be any significant voltage. That's the point!

[mrLEE30]

if you are getting funny readings on the above test make sure your meter is set to DC volts not AC! sometimes overlooked and can result in strange readings!

mrlee

[eltel]

thanks for all the advice...still havn't had time to check it yet ..but i will !!!