Dome light issues 04 prerunner.

Alrighty just got home! So I hate to ask, but given that my electronics knowledge is rudimentary at best, would it be possible for you to describe the process for conducting the checks you mentioned in detail? I have already checked everything from the fuse block all the way to the door switches, and I thought it was good, but I’d rather make sure I’m doing things correctly before I check again. Stuff like wether this is done with the truck on, fuse out, what setting to use on the multimeter, and wether to have the harness disconnected or back probe it for the test. Thanks!

 

New tires! Yay!

 

You know how to back prob, correct?

 

Yes sir, with connector in place you go from the back and contact the terminal with your probe.

 

OK, let me look over stuff and put together a check list.

 

Awesome thank you so much.

 

Do you have a test light?

 

1H Pin #10 - Power (12v) with door Open
1H Pin #9 - Ground with door Open

Testing the Ground Circuit
Hook the test light a known good 12v source. I like to use the battery, myself.
When backprobing the 1H connector pin #9 using the test light.
The light should come on when the door is open.

Testing The 12v Circuit.
Hook the test light to a known good ground.
With the test light on pin #10, the light should come on with the door open.

 

Nope

 

Correct me if I’m wrong, but both the DOOR and ON positions of the switch get 12 volts from pin 10. In the ON position the light works. Wouldn’t this be indicative of a ground issue for the DOOR position? In other words, the fault lies between pin 1 at the dome light switch connector, pin 3 at IG1, pin 9 at 1H?

 

Isn’t pin 10 constant 12 volts regardless of the door switches?

 

Any reason to use a test light over a multimeter meter?

 

How do we know the body ECU isn’t killing power for some unknown reason with the door open?

It certainly sounds like a ground issue, but we need to check everything thoroughly.

You could test the ground by using ohm or continuity setting in your meter.
But that won’t tell you if the ground can carry the load of the light.

 

Test light let you know the wiring is sufficient to carry a load. A single strand of wire will show good on a meter. But a single strand of wire will not carry a load.

 

Gotcha. Will make a test light at work today and let you know what I find! Hadn’t considered the ECU cutting the voltage with the door switches but that would make sense.

 

Probably a good idea to make my test light out of the same bulb as the dome light to simulate the correct draw?

 

You buy a cheap test light at any parts store for less than $10
Do NOT buy an LED test light. They don't draw enough current to be useful for 90% of testing.

 

Oh okay!

 

I have the same issue going on and have ignored it but looking into tackling it this weekend. I've done some checks and know that my ground is good. Where is the body ECU located at?

 

It’s the spot where your fuses are located next to your left knee. You have to get up under the dash to see the connectors for it.