Vauxhall Insignia reverse light and rear left indicator not working

Start by checking bulbs .

After checking your bulbs, or substituting a good bulb for the one that is not working and still the problem exists, check the contacts inside the bulb holders. You may find that they are corroded with either a greenish coating or a white powdery coating. Either way, you will need to clean off this coating, because this will prevent power reaching the various bulbs mentioned. Also check your fuses as sometimes a car is fused with seperate feeds for the right and left hand side of your vehicle. Check one thing at a time. Prove whether the bulbs are working first, then check the rest.