H3 headlights and driving lights going dim to bright

[Happy Hummer]

Overcast
-4°F
-20°C

Humidity	61%
Wind Speed	W 7 mph
Barometer	30.16 in (1023.4 mb)
Dewpoint	-14°F (-26°C)
Visibility	10.00 mi
Wind Chill	-18°F (-28°C)
Last update	14 Jan 11:53 pm CS

So, as the title states this just started tonight after the truck sat for several hours in the suburbs. I drove it today to the grocery store and back and it was fine, albeit it was day time so no headlights or driving lights were on. On the way home I allowed time for the H3 to warm up a bit and went very easy on it for the 1st ten minutes or so. Drove perfect! Went out to check on some properties and head back into town. When I got a few miles from home is when the lights started this weird dimming sh!t.
I had the headlights, driving lights, heater (setting 3) and the sound system bump'n.
Just replaced the altenator this summer... so unless it is funky... Checked the system with DVM when I got home and the system is putting out 14.13V With just the headlight.
With all lights and sound bump'n 14.20V. Hmmm! Not sure...

As posted above this is the current weather for my area. Never had this behavior with the old alternator'

 

[Happy Hummer]

By the way drove the H3 all day yesterday and it never skipped a beat. But it was about 25Deg's warmer.

 

[Happy Hummer]

Battery cable ends were done years ago. Battery was maintained this past summer. Actually removed the top covers and re juiced the fluid.

 

[alrock]

As you likely know, it's normal for the H3 lights to momentarily dim during use as the alternator kicks on/off. But if it's significant, it would sound like an issue with the alternator.

 

[Happy Hummer]

That would suck lol! It's a lengthy job. That's why I put an ACDel in it.

 

[Exodus]

before i replaced my alt,, every time i hit the brakes the headlights would slightly turn off, something like your problem

 

[Jeepwalker]

I would check:
1) Grounds - Grounds are so critical on modern vehicles. There are likely wire harness grounds up by the bulbs on the header panel. In rusty WI they can go bad. Check/clean any grounds, And, engine/body grounds as well as the + side.
2) Alternator Pulley - It's possible the alternator pulley grooves are worn causing it to slip unbeknownst to you. It can happen. Shouldn't be as likely since you replaced the Alt ...but you never know. Check it. If the ridges are 'sharp' replace the pulley. Normally they'd be flat between the grooves.
3) Belt - Same thing ...an bad alternator pulley, or one too loose, can slip and glaze or wear the belt in the wrong way and lead to slippage.
4) Alternator - Could be flaking out. Never know...those "rebuilt" jobs. They never last for me ...which is why I rebuild my own. If you remove it, get it tested. A lot of times a legit alternator shop with an old-school tester can just about tell you what's wrong when they hand it back to you. You can rebuild them too for not a whole lot. Or maybe there's nothing wrong with it. More than likely it's a ground/connection/wire issue. Or bulbs.

But if you have the alternator off, Pop off the back and inspect the brushes (I would probably do that before having it tested). Perhaps the brushes are worn ....or the commutator is badly worn. Brushes are cheap and easy to buy/replace. A guy can clean up a slightly worn commutator by chucking the armature in a drill press (use a wide flat file and then fine wet/dry sandpaper to clean the commutator). Repack the bearings, or replace with good SKF's. Rebuilt alterators don't seem to last as long as OEM, so that's one reason to rebuld. They use good Chineseum bearings/parts I'm sure. I've never had one I redid ever fail. Plus it's fun and educational (tons of y/t videos).
4) New bulbs can't hurt. They eventually loose their brightness anyway if they're pretty old. Check the connectors, etc

This is all just part of the *fun* and work of owning an old vehicle. Get used to having to deal with 'quirks'.

Good luck. Let us know the solution. Hope that helps.

 

[Happy Hummer]

It's a brand new acdelco right out the box genuine lol. The grounds c105 c106 multi splice are long since checked. The ground at battery long since checked. Pulley is brand new as it has less than 1k miles. Belt however is not brand new.
H3 never repeated the same behavior since this posting.
My truck is kept up as if it were my last defense during zombie apocalypse lol.

 

[Jeepwalker]

LOL ...ok sounds like you've looked into pretty deep.

 

[rascole]

Bad alternator would affect anything electrical, radio would quiet down (not bump'n), dash lights would dim, etc. Sounds like a chaffed wire on the light circuit leaking voltage intermittingly.

 

[Happy Hummer]

You have a good point wth stereo would be acting weird. Like wise all the lights internally. It was pretty much just headlights and driving light acting goofy.

 

[speedy]

Have you split the fuse box? Some have had issues with corrosion.

 

[Happy Hummer]

No lol haven't done that yet. I will have to give it till April to do that. Weather to unpredictable in February s.e. wi.