Headlights/Dash Lights Flickering

[239]

I noticed recently that my headlights and dash lights have a slight flicker at idle, when in drive. It goes away if I raise the rpm’s or if I turn the truck off.

I had the alternator tested and it was fine, but I noticed that when I tested with my multimeter the voltage would jump around. It never got low but would jump within the range of 14.3 and 14.5 volts a few times a second. It’s still charging my battery but I’ve also noticed a humming sound coming from under the hood.

I’ve cleaned where it mounts, and all the connectors up to the battery so the only thing I can think of now are bad cables.

 

[EB4X]

Your alternator should NOT be jumping a whole two tenths .3 - .5 ....only jump between mere one-hundreths... mine jumps from 14.5 2 to 14.5 3 ONLY.
Therefore I say your alternator is the cause of lights flickering (but electronics is not my specialty).... I had a cheapy refurbished one that started doing that a few months after install...it continued recharging the battery up until I sold her....had routine light flickering....had other fish to fry then deal with it at the time...hence just rolled with it.
When you tested yours did you pause long enough to make sure you had solid firm connections at both terminals long enough to get GOOD connected reading? I assume so...but just to rule out....

 

[239]

Your alternator should NOT be jumping a whole two tenths .3 - .5 ....only jump between mere one-hundreths... mine jumps from 14.5 2 to 14.5 3 ONLY.
Therefore I say your alternator is the cause of lights flickering (but electronics is not my specialty).... I had a cheapy refurbished one that started doing that a few months after install...continued recharging the battery up until I sold her....had routine light flickering....had other fish to fry then deal with it at the time...hence just rolled with it.
When you tested yours did you pause long enough to make sure you had solid firm connections at both terminals long enough to get GOOD connected reading? I assume so...but just to rule out....

It was tested while on the car and the battery was fully charged so I’m wondering if the auto store testing device doesn’t check for voltage regulator issues. I’ll drive it for a day or two since I cleaned all the connections. If I keep having issues I’ll replace it since it’s an aftermarket part that I installed in 2017. I also idle a lot so it definitely has wear.

 

[J_C]

I suspect either your meter isn't fast enough to pick up a lower voltage drop, or it's something else. It is unlikely that such a small drop from 14.5V to 14.3V for powering an incan bulb would be noticeable to the human eye.

If you're using the rearview mirror autolamps feature for the lights, I'd move the slider on it back and forth several times trying to wear away some oxidation and wear through old, hardened grease or use the dash switch to turn headlights on and see if that helps.

Bad cable, you can measure resistance with engine off, or with engine on you can measure for DC voltage drop between any two points. Any two points between which there is current flowing and a resistance in-between, there will be a voltage difference. Tiny difference means nothing, large difference means (most likely) corrosion of wire or connectors.

Humming, I'd try to find that first. Could be related or could be something unrelated that could still leave you stranded or cause more damage, though by damage it could be as simple as bad bearing, locks up something, that thing was dead anyway but it ruins the belt then soon the electronics freak out because the alternator isn't spinning to charge the battery. Hard to speculate, a lot of things can hum.

Another thing to look at is your belt tensioner. If the belt is too loose it may slip.