Dash lights dimming and brightening when headlights are off?

So when I turned my headlights off the other day my Stereo backlight started flashing from bright to dim. If I turn my headlights back on and the stereo backlight goes back to its standard dim setting it is fine. If I have the lights on and turn the dial up to brighten the backlight they work normally all the way to the brightest setting. It's only flashing when I turn the Headlights off. Once off, I have to dial the brightness down all the way and it'll stop flashing.

It's not a big deal for me as I run with my headlights on 99% of the time, but does anyone have any idea what might be up, or how to fix it? Thanks all!~

 

could be voltage regulator on the alternator going bad

 

Any specific suggestion on testing this? My truck is about 10 years old. Maybe a new alternator is in order?

 

Could also be (more likely IMO) a bad/corroded ground. Put a DVOM on the battery terminals with the engine running; at idle, you should see something north of 14.2v. That's by no means definitive, but it's a start as to the condition of your charging system. I would also have a look at wiring diagrams and see if there's a common ground for the stereo & other affected components.

 

With the engine at 2,000rpm, The Voltage should be between 13.2v-14.8v

 

I had this problem when I first bought my taco. When I hit the breaks my dash lit up. It was caused by an after market tow harness improperly installed and not grounded. Removed the tow harness and problem solved. Also threw a code and code went away as well

 

So I'm leaning towards it being something to do with just the Stereo backlighting, as that's the only light currently effected. And I tested it this time with the engine running and NOT running. Doesn't care which. Still flashes. And again, it is ONLY the backlighting on the JBL stereo "screen".

 

Those stereos start to go batty after a while. Mine did what yours is doing and then eventually the volume knob started bugging out (turning it would just randomly jump the volume around), and finally the buttons quit working about half the time.

 

Check the small ground wire going to the inner fender from the negative battery terminal.