Extreme dimming

[Kens1990K2500]

I haven't driven my truck much in a while, so I can't remember if it's always done this, or if this is a new problem (probably not a new problem, I'm thinking, since no recent electrical work). Anyway, I was driving after dusk and noticed that the brightness of the digital lights on my factory radio and heater controls, got really dim when I turned my headlights on (about 40 or 50 percent dimmer - very noticeable).

Is this normal? If not, what should I look for when troubleshooting? (Or if it is normal, what modifications can I do to prevent this from happening?)

Battery was replaced maybe six months ago, although the truck has not been driven regularly due to a long term project. I did start the truck maybe once a week and let it idle for 30 minutes to keep the battery from discharging, and, once I got the front end back together, drove it around the neighborhood a bit. Alternator is possibly original one, or at least it doesn't appear to have been replaced before I bought the truck three years ago.

My headlights don't seem especially dim, but I have never been able to see the road great at night, either. I just attributed it to old truck headlights, and my aging eyes. I did try using a headlight lens restoring kit; it made the lenses look better, but didn't improve road vision at night. I used to have a Honda with HID headlights, and those things were awesome.

 

[GoToGuy]

Really. Headlights off display defaults to bright for daylight. Headlights on display is tied into instrument lighting dimming function. Is this new to you, the instrument lighting control has been this way for 60 plus years.
If it does not react when adjusting lighting control ( dimming ) then you have a some malfunction.

 

[GoToGuy]

You also may need new halogen bulbs in truck headlights, as they age they don't put out as much light.

 

[Komet]

Yes they're supposed to dim with the lights on. Check the dimmer switch to make sure it's all the way up (before the click), sounds like yours may have been bumped.

Sylvania silverstars are an easy way to get more punch out of halogens. My wife still complains they're not HIDs but they're enough for me.

 

[Erik the Awful]

@Kens1990K2500, if the truck in question is a 1990 K2500 as your screen name suggests, the above posts don't apply. The later dash has dash lights on whenever the truck's running, but yours only lights up when the headlights are on.

It's most likely an issue with your cables and grounding. The factory battery cables were adequate when the truck was new, but with 33 years of oxidation they can't flow enough current to light up the headlights properly. Take a look at your battery terminals and if they're funky, you'll need to cut back to clean copper wiring, then install and heat shrink new terminal ends. Check the other ends where they bolt to the starter and frame and make sure they're clean and tight as well. Make sure your headlight wiring and dash wiring is clean and intact with clean ground wires. Personally, I replaced my battery cables with better wire.

If you want to upgrade you can either PM 5vortec7 about his "Big 3" kit, or you can build your own.

Big 3 and Dual Battery Kits

All set up to make kits!! Red and Black 1/0 gauge cable hex crimped with 5 ton crimper and soldered, then marine grade shrink wrapped. Here’s my first Dual battery kit I made for my 98 5.7

www.gmt400.com

He also has a headlight kit.

HD Headlight Harnesses w/ 4 High Mod

Here’s my version of the HD headlight harness. Delivers a full 12v to headlights through 12 awg wires. 4 high mod keeps low beams on with high beams. Made with all new materials, all connections crimped and soldered, ceramic headlight plugs, 30 amp inline fuses, 4 relay block with moveable...

www.gmt400.com

 

[GoToGuy]

Are you sure about that? Yes the headlight switch print is illuminated in the 95.
The radio display in the 93 is full bright with headlight switch off. Headlights on brightness of radio display is where the illumination headlight rheostat is positioned.
And everybody's night vision declines with age, a fact of life.

 

[Erik the Awful]

The instrument cluster in my '89 does not light unless the headlights are on. I know the '90 is a dial cluster instead of the moonies, but I'm pretty sure they don't light up.

 

[Kens1990K2500]

Thanks for the replies, both snarky and non-snarky.

Yes, the truck in question is a 1990 K2500. It does have the moonie gages.

Battery cables don't look horrible, but do appear to be original. As Erik suggested, I would eventually like to replace the battery and ground cables, possibly do the Big 3 upgrade. I did recently replace the engine to firewall ground strap.

And a headlight upgrade sounds in order also.

Till then, I will drink up on carrot juice and hope to get a lil' more traction out of these 55-year-old eyes.