sidelight playing up PLEASE HELP!!!!!

[sharding]

hi everybody... new here

I have a 406 hdi estate and ive lost my sidelights front + back . I replaced all bulbs and found that when I turn the sidelights on,
the rear bulbs illuminate very briefly and just fade out, then nothing????

ive done a bsi reset to see if this done anything but no luck.
made sure bulbs socket are free from any corrosion and theyre fine

kinda stuck now so need some help

not very mechanically/electrically minded so please bare with me if I struggle to understand any advice

[Malc]

Assuming this problem is while the car is running and not battery dependent and other lights function perfectly normal?
Sounds like a faulty positive outgoing or ground return on the sidelight circuit..
For starters I'd check battery negative for a good connection then go into engine compartment and carefully without any fuel pipe disconnection lift the fuel filter out the way giving access to the starter motor and the battery negative to ground connection..
Undo the (15mm I think) battery to ground connection clean then spray the nut and bolt termination with WD40 and tightly re-locate.
Old hat but worth a try as I can't see your symptoms being BSI..

[sharding]

Appreciate your reply. Will give it a look tomorow thank you