[dbenedictos]

Hi all! The dome light of my toyota corolla won’t turn on. Tried to measure the voltage drop, it reads 5v (when the doors are open), it reads 8v (when the doors are closed). Does anyone know why this happened? Thank you!

 

[Pete Suhman]

Probably contacts in the switch - especially where the metal 'bars' are riveted to the dome light shell.
You can remove the dome light assembly, and see if you're getting a full 12V from the wiring harness connector.

And welcome to TN!

 

[dbenedictos]

Probably contacts in the switch - especially where the metal 'bars' are riveted to the dome light shell.
You can remove the dome light assembly, and see if you're getting a full 12V from the wiring harness connector.

And welcome to TN!

Sorry I forgot to mention. Even from the wiring harness itself, I still get the same voltage drop. So I think the assembly is not the problem.

 

[JacRyann]

What's voltage at battery? Trace wiring from battery +12v and measure at every junction-point. At some point, you may find a drop, which indicates problem around that area.

Most likely a short against body near bulb-socket or dome light switch. Common problem. Short sucks away some of the voltage. Really bad short would drop voltage to zero at socket and blow fuses.

 

[75aces]

I'd look at the door switches at each door. It's located in the door jamb. It's a plunger with a connector behind the cover.