Volvo P1800 Interior Lights

I have noticed that the interior lights of my Volvo P1800 is not working. Today I checked for more detail, then only found out that there are NOT bulb inside the light panel.

I am not sure it if it missing just the bulb or the unit itself is faulty with no power reaching, so I got my voltmeter to do some measurement before buying a new bulb for it.

The test result is good, with 12V reading on the voltmeter.

Currently available bulbs in such bullet shape are mainly LED type. I wanted to get yellow type, but price is too high. Most common one are in white (daylight) colour. So I think it is OK.

I measure the distance between the two contacts, they are around 30mm. So I bought LED in 31mm type.