V1 Electrical question

[Ark :D]

Scenario: you have a multimeter, set to read voltage up to 20v max. You have a wire that's supposed to carry 12v. When you touch the positive probe of the multimeter to that wire, and touch the negative probe to ground, you see the expected 12v. But when you add a 12v light bulb to the circuit, you no longer read any voltage at all. What does this mean?

I noticed tonight, my right turn signal does not work now. First thing I did was test the bulb (it's not a bad bulb, it lights when given 12v). The next thing I did was get out my multimeter, and discovered the above scenario. Do I have a short?

 

[pisco]

The filament in the light is acting like a shunt, you have voltage but no current
Bad connection somewhere, I'd start on the ground side

 

[Ark :D]

It can't be the ground, because the running light in the mirror works fine. I'll trace the turn signal wire back to the BCM. Thanks.

 

[Ross]

Once you find the turn signal wire at BCM, re-test if it has 12V from the BCM to ground. It will help isolate where the bad connection is.

 

[Briann1177]

I agree with your assessment of having a short. Im not familiar with the internal electrical components of the mirrors, but my guess would be that something is going wrong internally when you plug the bulb in. My first hunch would be the lamp holder.

Swap your mirrors around and see if the problem follows.

 

[Rttoys]

swap mirrors and see what happens, like Briann said. That’s a quick Diag

 

[Ark :D]

It can't be the mirror though, because if I run a 12v wire (from the positive terminal of the battery) to the end of the turn signal wire on the mirror, it lights up fine.

I'll figure it out today. I need an excuse to not work on the honey-do list anyway.

 

[Rttoys]

never know if the bcm is being touchy little B...., if the mirror has a high resistance, the bcm may cut power to it to protect itself. You’ll never notice this with applying battery power to it, but through a computer, it may be a problem. It’s worth a quick try just to eliminate it.

 

[pisco]

With the lamp plugged into the socket ohm test the positive side to a known good ground elsewhere such as the batt terminal.
If it matches the other working side it eliminates the possibility it is inside the mirror.

 

[Ark :D]

The issue was, I had pinched that set of wires when I put my passenger side panel on. Once I found that, I fixed the wire and that was that.

Thank you guys.