ok this happens when im driving...ill be driving down the road and the headlights just kinda dim for a sec. and then go back to normal. anyone know why this may be happening?

 

Could be the alternator or the voltage regulator.

I had that happen too. I wanted a new V regulator but it was integrated w/ the alt. Ended up purchasing an alt. There is a core charge.

 

I replaced the alt. already. so that is brand new. i thought i read somewhere before that it could be that the belt is loose and slipping and this may cause it. Is this possible?

 

If your alternator/regulator is good, then your head light ckt has picked up a higher resitance than it should have and when your alternator is actively charging, thing seem fine. When the alternator (regulator in alternator) takes a short break, this high resistance shows up and causes a dimmer lite situation.

lots of things can cause this. Check your belts and tensioner, though I doubt this is the problem. Never bad to replace an old belt anyway.

Any oil under the hood in places it doesnt belong? Does the alternator get hit by flying oil or did you spill any on it? No faster way to ruin an alternator and also the most common reason for their failure. Had an old 2.5 that would spit oil out of the front seal and it always made its way up to the alternator by way of the belt. Replaced those alternators about every 6 months, The parts store hated me. No way I was fixing the darn thing though, Ran 325000 miles and it was actually involved in an accident before going to junkyard, not engine failure. I had given it away, before that happened.

So back to bad ckts and lamps. Lights themselves wear out and even look funny when they do. Is one of your lites dimmer or darker than the other? Did you replace the other one? Doing both is better, though not normally done.

Had any body repairs that might affect ground ckts? Have you pulled off connections at bulbs to check for corrosion?

Is the wire going TO the battery FRom the alternator a nice heavy one? 10 I think is factory, 8 or 6 is better. Is terminal in good shape?? At BOTH ends?? Is battery cable of original variety or replacement with crimp, to alternator? Crimps are great places for resistance buildup. (bad connection), Those cheap big yellow butt connectors, supplied on aftermarket battery cables, are a great place for trouble. Run wire DIRECT from battery to Alternator.

Bad connections to the battery are a natural and first place to check. BOTH battery and ground. DONT SKIP GROUNDS. Check ENGINE ground.


Any bad ckt, even in the back, such as corroded bulb holders (in back) can cause problems, make sure to check the rear lites. BTW some model blazers had real problems with rear lites.


Is alternator case bolted properly and conducting to ground correctly? Believe it or not, this all aluminum stuff and tensioners lead to things being loose without anyone actually knowing it.


In the long run, if for no other reason than it is a better way to lite up your headlites, reinstall the headlamp ckt. Needed is a relay with a DIRECT source from the battery (positive) to be switched to the headlamps, directly. Install is the same as for a set of driving lights. The operate path should be directly from the same path that used to go to your lites. Just operate the relay from the original lite switch and wiring. Then the path for electricity is direct from battery rather than passing through the lite switch and back again, through all the thin skinny wire originally decided were great for those yellowish 6 volt bulbs we used to use long ago.

I used to own an old chevy van that would brighten and dim as I hit bumps. I knew why, just didnt fix it. Interesting to strangers though. This was a ground strap going bad, but this should not happen to modern ckts such as yours, though I would certainly check your engine and chassis grounds very thoroughly.

 

thanks for all that info. blazingsadle. ill check it out and comeback with what i discover