Get yourself a multi meter and test the bulbs, This one under £10 it will also detect buried cables!

 

https://www.amazon.co.uk/Multimeter-Auto-ranging-Electrical-Transistor-Continuity/dp/B01MXGOCOF/ref=sr_1_2?ie=UTF8&qid=1529930609&sr=8-2&keywords=multimeter+with+continuity+buzzer

Edited 25 June, 20188 yr by gumdrop

Just now, gumdrop said:

Get yourself a multi meter and test the bulbs, This one under £10

 

https://www.amazon.co.uk/Multimeter-Auto-ranging-Electrical-Transistor-Continuity/dp/B01MXGOCOF/ref=sr_1_2?ie=UTF8&qid=1529930609&sr=8-2&keywords=multimeter+with+continuity+buzzer

I have two very good multimeters, they will tell when a lamp is open circuit, however the resistance difference between a good lamp and a bad (not blown) lamp is quite small and you would need a new lamp for comparison. Just not worth the effort its as easy to change lamps.

38 minutes ago, idleness said:

I have two very good multimeters, they will tell when a lamp is open circuit, however the resistance difference between a good lamp and a bad (not blown) lamp is quite small and you would need a new lamp for comparison. Just not worth the effort its as easy to change lamps.

 

I did mean test for continuity , a meter is a very reasonably priced tool for the car and for the home,

even if they cannot use one themselves there is often someone around who can.

I changed all the bulbs on the one side and then the following day I had a bulb go on the other side and I just thought sod it so once again I changed all the bulbs, and touch wood not had any more problems with any bulbs