Headlights and Instrument Panel Flickering

[FJ4013]

My rig is a 1978 FJ 40.

I've noticed recently at night when driving my headlights are dimming and brightening and my instrument panel is as well. It is not a rapid dimming and brightening but it's not exactly slow either.

Any ides what is causing this?

UPDATE: Culprit identified as the battery. Had a full check and the battery is bad. Replaced it and the flickering is now gone.

 

[1969FJ]

Give more information about the vehicle and its' electrical system.

 

[FJ4013]

Give more information about the vehicle and its' electrical system.

1978 FJ40
As far as I know the electrical system appears to be OEM. When I rev the engine the headlights get slightly brighter at times. Alternator going out maybe?

 

[want2wheel]

Check and make sure that the ground is good and solid from the frame to the engine, and the battery ground connection is good. Then check and see how may amps the alternator is putting out. Depending on where you are you can go by an auto parts store and they will do a full load test on it to check the charging system.

 

[Burbot]

Check that idle is correct, not to lo. Belts are tight and grounds are clean and solid. Run all your accessories can alt. keep up? Did it previously?also how's your battery. I ran all new grounds on my 24v. Bj and it made a small difference. Then a load test as advised

Ah might as well get some pictures of these.

View attachment 1459959 View attachment 1459960

Did some work

View attachment 1524563

Check and make sure that the ground is good and solid from the frame to the engine, and the battery ground connection is good. Then check and see how may amps the alternator is putting out. Depending on where you are you can go by an auto parts store and they will do a full load test on it to check the charging system.

 

[FJ4013]

Check and make sure that the ground is good and solid from the frame to the engine, and the battery ground connection is good. Then check and see how may amps the alternator is putting out. Depending on where you are you can go by an auto parts store and they will do a full load test on it to check the charging system.

I've checked the ground and it is solid. Checked all connections and cannot find any issues. No corrosion. Everything is clean. Just old. I will try to get a full load test today. My gut tells me it is the alt.

 

[beecherjeeper]

• To check for a possible bad alternator diode, switch your voltmeter to a low setting on the AC (alternating current) voltage scale.
• With the engine running, touch the meter probes to the battery terminals—positive (red) meter probe to the battery positive terminal, and negative (black) meter probe to the battery negative terminal.
• Your voltmeter should read 0 AC volts.

The presence of even a small amount of AC voltage will indicate a bad diode, so you'll need to replace the alternator's rectifier or the alternator.

 

[FJ4013]

• To check for a possible bad alternator diode, switch your voltmeter to a low setting on the AC (alternating current) voltage scale.
• With the engine running, touch the meter probes to the battery terminals—positive (red) meter probe to the battery positive terminal, and negative (black) meter probe to the battery negative terminal.
• Your voltmeter should read 0 AC volts.

The presence of even a small amount of AC voltage will indicate a bad diode, so you'll need to replace the alternator's rectifier or the alternator.

Good to know. Thanks.

 

[thebigredrocker]

@bj40green has posted good VR info
Voltage Regulator (ext.) / How it works

 

[FJ4013]

@bj40green has posted good VR info
Voltage Regulator (ext.) / How it works

Thank you. Good stuff!

 

[bj40green]

The alternator is putting out only a few amps at idle. Just enough to keep the basics (ignition, running lights, hazard lights) going. Turning on your headlights at idle makes the voltage drop a bit. When you rev up above 1000 rpm the alternator gives full output. That's why the brightness of your headlights goes up and down.
Reminder: this is 70's technology!

Rudi

 

[FJ4013]

The alternator is putting out only a few amps at idle. Just enough to keep the basics (ignition, running lights, hazard lights) going. Turning on your headlights at idle makes the voltage drop a bit. When you rev up above 1000 rpm the alternator gives full output. That's why the brightness of your headlights goes up and down.
Reminder: this is 70's technology!

Rudi

So the dimming and brightening is normal?

 

[bj40green]

So the dimming and brightening is normal?

Yes. What also adds to the problem is the small wire sizes used by Mr. T.
If you add 2 relays and feed them with an inline fuse directly from the battery it will improve the brightness a lot.

NOTE: This diagram is for a system where the headlight switch is grounding the circuit.


Rudi

 

[FJ4013]

Yes. What also adds to the problem is the small wire sizes used by Mr. T.
If you add 2 relays and feed them with an inline fuse directly from the battery it will improve the brightness a lot.
View attachment 1525900

Rudi

Currently I have only one ground coming from the battery. You recommended configuration would require me to run another ground or not? I am not an electrical wiring expert by any stretch so please assume I am a 3rd grader with respects to this.