Dome light Dilemmas!

Hi all new here and not sure if this has been covered but couldn’t find anything in a search.
I have a 2002 Jimny cabrio (new to me) and am trying to iron out some wrinkles. 
the one at the moment that is really getting to me is the dome light. The passenger door works fine, but for some reason the drivers door  doesn’t. The switch tests ok, and the cable checks out all the way to the connector behind the glovebox. The only oddities I can find are that a.) when testing the driver’s door switch I notice a 12v circuit on this switch- I was not expecting a reading as I thought the whole line was negative/earth? Is this normal? It doesn’t blow fuses so I am assuming so.
b.)  I’ve noticed the drivers door runs through a diode before going to the dome ( connector g06) above the glovebox box if this has blown it would make sense that the circuit would be broken, but then why do I see 12v on the line? If I bypass this diode will I cause other issues?
has anyone replaced this diode? A google search only wants to find references to alternators when you reference diodes & vehicles.
does anyone know the part number to replace the diode - or what the value of the diode would be?
any help very much appreciated.
thanks

Keir
 

A defective diode is a possible cause of your problem, the reason the diode is there is because the dome light circuit is one of several circuits that are triggered by that switch, and you don't want the other circuits triggered by the other door switches.

If you're seeing 12V on the switch wire it means the switch is either not closed, not grounded or there's a broken wire somewhere in the circuit.

Have you tried swapping the switches over 
So drivers side works and passenger will then be intermittent 

My driver side works passenger intermittent 

Thanks Fordem
Figured this could be it. Interestingly I have no warning buzzer for lights keys etc. I guessed that the diode was linked to these systems.
Unfortunately the circuit diagram is at best vague when looking for the controller but as far as I can see it’s part of the instrument cluster - this can wait! I’ll try to find a replacement diode and go from there.

To be honest I hadn’t as it tested ok on the metre but now you mention it I will as I have had things test up ok before but not actually work.

No warning buzzer AND no dome light strongly suggests a problem with the switch and or the wiring and this is more or less confirmed if you're seeing 12V on the switch wire.

IF the switch is working & properly grounded you will not see 12V on the wire with the door open.