Interior lights / door jamb switches

[orkenny]

Good morning all, this is my first post on what looks to be a great source of knowledge. I am not an electrician but I do enjoy trying to sort these little issues but I am not sure where to start with this.
I have a 2007 Isuzu pick up. The interior lights do not come on when the doors are opened. The 2 lights do work as they can be switched on and yes I've made sure the switch is set to work when doors are opened. I've put a meter on each of the 4 door switches. I get 12v at drivers door and only about 0.4 at each of the other 3 so something is amiss there. When I activate the switches the reading drops so I guess the switches are functioning? Does this sound like an earth issue somewhere?
Any help or ideas where to look would be much appreciated.

 

[telectrix]

basically, the lights have a permanent +12v to 1 side. when a door is opened, it shorts the other side to 0V. with a door open, you should not see +12V at the door switch.

 

[orkenny]

basically, the lights have a permanent +12v to 1 side. when a door is opened, it shorts the other side to 0V. with a door open, you should not see +12V at the door switch.

Thanks telectrix. So could my drivers door switch be the problem?

 

[orkenny]

Update... I have 12v at the supply to the driver's switch and 2v on the switch.

 

[orkenny]

Update... I have 12v at the supply to the driver's switch and 2v on the switch.

And also the dash light doesn't come on when a door is open

 

[KEV 1 N]

basically, the lights have a permanent +12v to 1 side. when a door is opened, it shorts the other side to 0V. with a door open, you should not see +12V at the door switch.

Not necessarily, this was the case on older cars, but new cars are different, as the interior lights come on when the car is unlocked and fade off / time delay when doors shut etc. The diagram below is from a Vauxhall and 41 shows the interior light, as you can see there is only one earth supply to the light and multiple positive feeds to activate the lights when doors opened, switch set to “on” etc.
Check wiring connections at light fitting first