No Lo/Hi beams & battery discharge/overcharge while driving
 

Hello! First time poster. Very lost on what's going on with my 96 4wd 2 door Blazer.

Just to get things out of the way I have checked all fuses and none are broken, though for a while the ecm/battery fuse would blow if I attempted to accelerate too fast from a stop. This has not happened in a couple months but wanted to mention it for reference just in case.

Recently both the low and high beams went out. I have DRLs and parking lights. On occasion the DRLs disappear. They'll come back on again later. Best I can come up with is perhaps a break in a wire or a bad ground, but I'm new to electric work on vehicles. I checked the headlamp switch, its a bit worn inside but the copper contacts seem to connect still. This weekend I am going to make sure it's getting power. I have been at work and haven't had time to go to my dad's shop this week.

As for the battery issue... sometimes when I am going above 60mph, the battery light comes on, and the volt meter suddenly lurches towards 18v. Once in a while the left turn dash indicator comes on solid too while this is happening (sometimes only its own though. Goes away if you let off gas). It tends to happen when accelerating, and if I immediately let off the gas, it will all go away. The air bag light also interacts with this, often being off or solid, but blinking rapidly when this battery light issue occurs.

If the gas is not let off in time and the voltmeter hits 18v, a sharp pang happens in the vehicle. After this, shifting from 1st to 2nd gear becomes an extremely hard shift. If the vehicle is shut off and immediately started back up at any point, the hard shifting from 1st to 2nd is gone until the battery thing occurs again.

On rare occasions, usually between 50mph and 60mph the same sort of thing will happen except the voltmeter will go down towards 9v, and if I let off the gas it once again rights itself.

Very strange issue. Couldn't find anything on it anywhere I've tried searching quite a bit.

I also have access to AllDataDIY for my blazer, its more a matter of me learning which diagrams to use and how to read them. Anything to point me in the right direction would be appreciated, I'd really like to have both issues resolved this Saturday and/or Sunday. Thanks in advance, and I'm glad this site is around. Its helped a lot in the past.

You need to see what is happening with the system voltage while all of this is happening. Either run meter cables/wires into the cab or get a cigarette lighter meter.

While your doing that, make sure all your alternator and battery cable connections are clean and tight including the battery ground cable at both ends.

George

:icon_ditto: What George said.

It sounds likely to be a ground issue to me, but you need to monitor the voltage while it's happening to help diagnose and trace the source of the issue. Follow George's advice and he'll help get you there.

Headlights still Sporadic
 

The battery issue is now resolved. I believe it was the voltage regulator in the alternator. I replaced the alternator completely as it was pretty old, and then also got a new battery because the other one had been over and undercharged enough times it was no longer reliable. So voltage issues are gone.

Headlights are still doing their thing though. I always have DRLs, but hi/lo beams are sporadic. I didnt have them for 2-3 weeks, then they came back for a couple days. Gone for a week. Back for two. Tonight they went out again.

Im trying to figure out where the grounds are on this thing but im just not very experienced with cars outside of regular maintenance and speaker installation and so the plethora of wires is confusing me. I know what a ground looks like but cant seem to find many on the thing, I have access to diagrams but going from a diagram to the actual vehicle without a "real life" visual pointing out certain wire clusters are has made it hard for me.

The headlights appear to start working again when it has rained. I cant guarantee this makes them "work" but then working tends to coincide with it having been very wet outside on a given day.

I have checked the rocker switch twice, gotten rid of the corrosion, cleaned and shined the contacts up and nothing so I doubt its that. I haven't looked at the multifunction switch stuff yet as I haven't had time but I wondered if that was the next step.

Sorry for the long windedness, I just try to be thorough. I really do want to learn more as I try to fix everything on my own to both learn more and save some money.

Do you have sealed beam or the composite headlight version?

George

They are sealed. I couldn't figure it out at first but apparently they say SEALED BEAM in all caps on them.

Last night, a light bump with my hand on the rocker switch turned the headlights on.

Tonight, they were on when I arrived where I was going, were off upon starting the vehicle again, and then after letting the vehicle idle for a couple minutes they came on on their own.

Last night has me wondering if it is in fact the rocker switch getting stuck or something. I messed with it again last night and seem to have slightly more consistency with getting my headlights on but im honestly still pretty baffled.

You have two choices. First would be the parts cannon which I am generally not a fan of but if tapping the headlight switch makes the headlights turn on then maybe its reasonable to replace the switch.

The other approach is to travel with a voltmeter and start testing key points when its acting up. Is it easy to pull that switch out so that you can get some voltage readings?

George