Vw polo left indicator light stays on when lights are on

https://www.youtube.com/watch?v=SQTDr3up0Hw

oil pressure switch faulty

More than likely its bulbs .

you have a bad ground in the left taillight unit, so whenever lights are used the circuit loops back instead of going to ground, good luck to you

It sound like you have a grounding problem, does the headlight on the left seem dimmer than the right? Check the ground wires and the light sockets for corrosion.

make sure our lights at rear are grounded sounds like a bad earth

battery terminals loose?bad ground?short?

first clean throttle body out with carb cleaner and some clean cloth , if the throttle flap is dirty the car will stall

I bought a 2000 polo 1.4 yesterday after having an MOT. The warning lamp came on today but the car is running fine. Whether its the Lambda sensor or just the light itself is a common fault, I think garages turn off the lights to get it through the MOT then they come on again in a day or two!