240 Voltmeter jumping

Hello all,

I recently did the hard wiring of taillights modification, because my taillights broke for the 4th time in a few years. I'm not sure if this issue started happening before or after I did this, but I really started noticing it recently.

When I use my blinker on either side, my voltmeter jumps about 1/4 of the gauge. It seems to oscillate with the blinker, going down ~1/4 of the gauge when the blinker turns on, and then going back to where it was when it turns off. The voltmeter also seems to go down a lot when I turn my lights on also.

Does anyone know what could be causing this?

- Bryan

Does the blinker bulb light up? It sounds like a short circuit somewhere but if a fuse isn't blowing that may not be it. Does the fuse get hot?

I'd start by checking the current the blinker circuit uses at the fuse using a multi-meter

You may be having problems with your alternator.

With the engine idling check the voltage with a volt meter .
The voltage should hover around 13-14 volts.

Have someone turn the headlights on while watching the meter.

The voltage shouldn't drop below 12.5-13 volts.....at least not below resting battery voltage.
This is the battery voltage with everything cut off....even the engine.

A weak battery can also cause some of your symptoms.
I suspect that this is your problem.
How does the starter spin the engine? Strong and fast, or slow and dragging?

A flashing light will always cause some fluctuation in voltage.
The simple fact of the current changing as the bulb illuminates and darkens will cause this.

coalminer said:

You may be having problems with your alternator.

With the engine idling check the voltage with a volt meter .
The voltage should hover around 13-14 volts.

Have someone turn the headlights on while watching the meter.

The voltage shouldn't drop below 12.5-13 volts.....at least not below resting battery voltage.
This is the battery voltage with everything cut off....even the engine.

A weak battery can also cause some of your symptoms.
I suspect that this is your problem.
How does the starter spin the engine? Strong and fast, or slow and dragging?

A flashing light will always cause some fluctuation in voltage.
The simple fact of the current changing as the bulb illuminates and darkens will cause this.

Click to expand...

if you have ever seen this: https://drive.google.com/file/d/0B_GPQ_U91zlDaXlZMVlHYm04aGs/view?usp=sharing

thats also a sign of an alternator going bad.

esmth said:

Does the blinker bulb light up? It sounds like a short circuit somewhere but if a fuse isn't blowing that may not be it. Does the fuse get hot?

I'd start by checking the current the blinker circuit uses at the fuse using a multi-meter

Click to expand...

Yes the blinker bulb lights up when I use the turn signal, what voltage should I be looking for from the blinker fuse?

coalminer said:

You may be having problems with your alternator.

With the engine idling check the voltage with a volt meter .
The voltage should hover around 13-14 volts.

Have someone turn the headlights on while watching the meter.

The voltage shouldn't drop below 12.5-13 volts.....at least not below resting battery voltage.
This is the battery voltage with everything cut off....even the engine.

A weak battery can also cause some of your symptoms.
I suspect that this is your problem.
How does the starter spin the engine? Strong and fast, or slow and dragging?

A flashing light will always cause some fluctuation in voltage.
The simple fact of the current changing as the bulb illuminates and darkens will cause this.

Click to expand...

A while ago I had alternator issues, where the car would almost die if I was sitting at a light for a while. I took it to a mechanic and he replaced the brushes in my alternator, I believe that was about a year ago. Currently the car starts great, it doesn't start the millisecond I turn the key, but I only have to have it turned for maybe 1 or 1.5 seconds before it starts.

I understand that anything using the system could cause the volts to go down a little bit, it just doesn't seem right that it would go down 1/4 of the meter when I use my blinker.

I'll check the volts on my car later today, and report back my findings.

Also I'm not sure if this has anything to do with it, but I had my engine wiring harness replaced about 1 year ago. I'm just trying to think of anything major I had done fairly recently.

Bcmonks said:

Yes the blinker bulb lights up when I use the turn signal, what voltage should I be looking for from the blinker fuse?

Click to expand...

You're looking for current, not voltage, and if it's more than 4 amps there's a problem

I don't know what kind of voltmeter you are looking at. But a non dampened voltmeter movement will fluctuate more than a dampened movement in the gauge. You may also need some help in your car electrical system like making sure there is a good clean ground on the alternator to engine and from the block to the battery. Also the battery to inner fender is another very important ground to make sure it is clean and tight.

dl242gt said:

I don't know what kind of voltmeter you are looking at. But a non dampened voltmeter movement will fluctuate more than a dampened movement in the gauge. You may also need some help in your car electrical system like making sure there is a good clean ground on the alternator to engine and from the block to the battery. Also the battery to inner fender is another very important ground to make sure it is clean and tight.

Click to expand...

I assumed it was the Volvo 240 52mm volt meter which is dampened, or at least mine was

Try spinning fuse 13 -- both the turn signals and the voltmeter go through #13.

You can also try turning on the 4-way/emergency blinkers and see if the voltmeter is steady - the 4-ways are fed by fuse #9.

esmth said:

Does the blinker bulb light up? It sounds like a short circuit somewhere but if a fuse isn't blowing that may not be it. Does the fuse get hot?

I'd start by checking the current the blinker circuit uses at the fuse using a multi-meter

Click to expand...

This.

bobxyz said:

Try spinning fuse 13 -- both the turn signals and the voltmeter go through #13.

You can also try turning on the 4-way/emergency blinkers and see if the voltmeter is steady - the 4-ways are fed by fuse #9.

Click to expand...

I tried exactly what you said and it fixed it instantly. The hazards had almost no drain, and when I changed fuse 13, the problem went away.

Thank you all for you help, without you guys I would have still been afraid to go out at night due to the car possibly dying.