When i turn my lights on i hear this noise

[CARGUY40]

So i went to the mechanic today to see if he can figure out what this noise is. When i turn my lights on you hear it very little like hardly but then with my lights on foot on the break and i put it in drive or reverse its louder like squeaky. He tested the alternator and battery and said those are fine and he thinks its one of my pulleys but how can it be the pulley when the noise is not there at all when my lights are off? Even when im in drive with the lights off there is no noise. What do you guys think? Does the pulley have to work harder when im in drive and the lights are on?

1994 Infiniti J30 3.0 111k miles

 

[PeterPolyol]

Describe the noise as best you can

 

[koffy]

Lights on mean an extra load for the aternator (harder to rotare).
It might be a Nissan thing, my xterra vibrate a little bit more when I turn on the lights,
You can try with a diferent load such as windows switches or rear defogger to see if you heare the same noise

 

[eljefino]

Well the belt will have more tension on it so yeah an unrelated pulley elsewhere on the belt can squeak.

 

[Pop_Rivit]

Get your mechanic's stethoscope out, start the car, turn on the lights, and find out what's causing the noise. Then fix it.

Simple.

 

[edwardh1]

put some soap on the belt, rub a bar of soap on the belt (carefully) , see if noise changes

 

[bioburner]

I have the issue with the used motor that I put in the Transit when I engage the AC. Mechanic and I have found it to be a idler. PIA of course to get to. IF an issue when cooling season comes will attempt to get to it and put in new bearings.
This will be the 4th vehicle I have had that an idler has had issues.

 

[Olas]

Originally Posted By: Pop_Rivit
Get your mechanic's stethoscope out, start the car, turn on the lights, and find out what's causing the noise. Then fix it.

Simple.


This!

 

[HerrStig]

Originally Posted By: edwardh1
put some soap on the belt, rub a bar of soap on the belt (carefully) , see if noise changes
The belt may then slip forever after.

 

[mclasser]

Originally Posted By: Olas
Originally Posted By: Pop_Rivit
Get your mechanic's stethoscope out, start the car, turn on the lights, and find out what's causing the noise. Then fix it.

Simple.


This!

+2 Even a long screwdriver works. But of course, be careful.

 

[CARGUY40]

So the answer is yes to when the lights are on and im in drive or reverse that makes the pulleys or belts work harder causing the pulley to make noise meaning it needs to be replaced or my belts need to be replaced?

 

[PeterPolyol]

If it's a loud screeching noise that that all your neighbours can hear then yes the belt is slipping. Also, yes, electrical load makes the alternator harder to turn and will expose an improperly tensioned belt.

 

[mk378]

The answer is yes.

Putting the car in drive or reverse lowers the rpm. As the rpm drops the alternator needs more torque to make the same amount of electricity (if it even can).

Each #1156 (reverse lights) or 1157 (brake lights) bulb uses about 25 watts of power. A halogen headlight bulb is 45 to 60 watts. If you have four brake lights and a center light, putting the car in reverse and holding the brakes down takes more electricity than the headlights.

 

[CARGUY40]

So its possible the alternator is making noise when i turn the lights on and put it in gear? is it possible the belt is old and causing the noise when there is heavy load?

 

[artificialist]

An old belt may be causing this, but always check the belt tensioner when there is a slipping belt. Failing tensioners may develop bearing noise, or they may fail to keep enough tension on the belt.

Idler pulleys can also be a cause of the noise if bearings are failing.

I often see tensioner and idler parts fail when cars are 15 years old, so it wouldn't surprise me if you needed several different pulleys.