Rear fog light gives 7,9V

[Tynisteri]

I bought a used rear fog light switch from ovoko. Seems like i ordered a worthless piece.

Could it be wires or is the switch just super bad?

also when one fog light is on the volt is something like 0.0007 and when both are without lights it returns to 7.97V.

[ColinBarber]

I'd remove the switch and check resistance across pins 1 and 3 confirm if it is working or not. Also check the fuses that feed the circuit aren't cracked.

Possibly you have a bad earth at the lights?

[Herbie]

This has all the hallmarks of a bad earth so unbolt it and clean up both the bolt itself, any washers, and also where it bolts into the body, with wire wool or emery paper so that the connection is clean and shiny.

[Tynisteri]

2 hours ago, Herbie said:

This has all the hallmarks of a bad earth so unbolt it and clean up both the bolt itself, any washers, and also where it bolts into the body, with wire wool or emery paper so that the connection is clean and shiny.

Where is the place where earth is bolted?

[Tynisteri]

I checked how many volts does the wire get before light bulbs and its 11.97v.

i think maybe light bulbs take some voltage so it isnt 12

[Herbie]

3 hours ago, Tynisteri said:

Where is the place where earth is bolted?

Usually somewhere close to the item you're trying to troubleshoot.

[ColinBarber]

17 hours ago, Tynisteri said:

I checked how many volts does the wire get before light bulbs and its 11.97v.

i think maybe light bulbs take some voltage so it isnt 12

The light bulb should take all of the voltage, which is why you should expect the full 12v to be across the bulb.

Without a picture of exactly where you are measuring it is difficult to tell where the problem is, but it seems there is possibly a bad earth (although that is likely to affect multiple lights) or corrosion in the bulb holder. If you want to eliminate an earth issue without having to trace the wiring then use a spare piece of wire and use it to create your own temporary earth, ideally directly connected to the battery's -ve terminal if you have wire long enough, or from a clean metal point on the body somewhere.

[Tynisteri]

I messured it from the left lower side of the trunk.

i cant find the place where earth is, is there maybe a picture or a map?

On 9/17/2024 at 2:54 PM, Herbie said:

This has all the hallmarks of a bad earth so unbolt it and clean up both the bolt itself, any washers, and also where it bolts into the body, with wire wool or emery paper so that the connection is clean and shiny.

 

10 hours ago, ColinBarber said:

The light bulb should take all of the voltage, which is why you should expect the full 12v to be across the bulb.

Without a picture of exactly where you are measuring it is difficult to tell where the problem is, but it seems there is possibly a bad earth (although that is likely to affect multiple lights) or corrosion in the bulb holder. If you want to eliminate an earth issue without having to trace the wiring then use a spare piece of wire and use it to create your own temporary earth, ideally directly connected to the battery's -ve terminal if you have wire long enough, or from a clean metal point on the body somewhere.