in this cold. main beam makes engine nearly stall m40 1.6

[arrisbmw]

Hi All, anyone had this before. yesterday drove 50 miles lovely no issues. on jouney home car starts o.k but when i put main beam on engine dies. weid. on the 50 mile drive home, car was not running right seem to be mis firing and jerky. run better with the headlights off. any ideas please. i checked the battery today showed 12 volts only went down to 10 v on cranking and shows 14v on multimeter when engine running.
thanks in advance

[arrisbmw]

is it possible , that load on the alternator slow the engine ?

[Jesus325iTouring]

Sounds like a battery issue, though could be linked to a bad earth. Have you checked main engine - body earth strap?

[arrisbmw]

oh thanks, where is that located please.
yes when i fully charged the BATTERY , stood for a week or so and was less that 12.6 volts.

[Jesus325iTouring]

I can't remember exactly, but if memory serves me right, on the right hand side, close to the bottom of the engine. Don't quote me though, been a long time since I had last looked at one! It will be obvious though.

[arrisbmw]

updt . new battery fitted . done the job 63 ah 600cca .