Well heck, search is disabled; I was hoping not to bother anyone with another of my weird problems.

My battery light came on the other night while driving home. It had been raining medium hard for almost 24 hours here, it was like living underwater. At highway speed the light went off. It stayed off when stopped at a stop sign. Then it came on again at highway speed. Then it started to come on intermittently. I cleaned the battery terminals real good (they needed it anyway)The light still stayed on. I went to run some errands and it went off. On the way home it came on at highway speeds and then went back off again. This morning it came on but went off after about 15 minutes of running and has stayed off until now.

Amp meter on the dash has stayed right up where it is supposed to be. Could this be some kind of relay going bad? A voltage regulator? The owner's book says the charging system failing is what makes the light come on. (yeah, really helpful... not) Otherwise the rig runs as great as it always has.

Any ideas??

Thanks, CedricR.

 

I've had this happen in the past and it turned out to be the alternator. These trucks have an idler wheel style of tensioner and they tend to wear out the rear bearing of the alternator causing the voltage to vary. If not mistaken, both overvoltage and undervoltage can cause the battery light to come on.

 

The book is right, your charging system is failing. It sounds like an intermitant failure but will likely fail permanent. Does the volt meter (Not amp) in the dash go down when the light comes on?

HAve the charging system checked at Autozone or murrays or any one of the chain-type auto parts store. It could be something as easy as a bad connection on the alternator too. I betting on a failing alternator, the regulator is internal.

 

It probably just needs an alternator. Mine did that exact same thing for a month or so. It always started and ran fine. I finally took it off to get it tested. Advance auto tested it for free- it was bad.

 

The volt (not amp) meter reads steady right in the middle of the range. I expect that the light is a great deal more sensitive to variations. I'll go off to Advance tomorrow.

Like I ain't got nuthin' else to do.
CedricR.

 

Most likely the alternator, like the others said. The reason the light seemed to go off at higher speeds is that it's turning faster and outputting more current. I had an alt going bad on a little toyota once... it did okay at freeway speeds, headlights were dim, but as I slowed for an exit, they cut out altogether. Then as I rolled into a gas station, the engine cut off. That wasn't a fun time.

You can do a check that's a bit more accurate than the stock volts gauge. Here's what I learned from dealing with that toyota: Take a digital volt meter and check the battery with it when the engine is not running. Should be around 12.5 volts. Now start the engine and retest: should be around 14.5+ volts if it's charging properly. My guess is you'll be getting less, if the alt isn't working properly at that time, like probably 12 volts or less. If that is the case when you test, or if the light keeps coming on, address it ASAP or you'll be stranded once your batts run out of juice. Also wouldn't hurt to get the batts load tested at Autozone... could be the batteries aren't holding a charge... but I still suspect the alt, first.

Also, running on a bad alt... if you let the batt run down, then recharge it, then it runs down, then recharge it... while putting off replacing the alternator, it will eventually kill the batteries, too.

I might as well share the rest of that story about that little '90 toyota celica, my first car, when I was about 18 years old.

Here's how it started: I got stranded twice. The first time, I was on my way down a windy mountainy road from a friend's house way across the SF Bay, at about midnight, when the problem very first showed up. My battery light came on, and my headlights started dimming like crazy. Right as I get to the bottom and am passing a hotel, the engine cuts right out. I swing into the hotel parking lot. I was able to call and have my mother bring a battery charger out to me (what a dear) as I checked on a tow and it would've been hundreds of dollars, so I pulled the battery, dragged it over to near the hotel soda machine (quietly, as it was right outside the manager's room), and plugged it in for about 5 hours overnight. Slept in the car. Put the batt back in the next morning, at about 6am (before anyone from the hotel could catch me plugging my battery charger and battery into their wall next to their soda machine ), and drove the 1.5 hrs home. I had to shut off the headlights about 5 miles from home as they were dimming, and didn't want my engine to cut out again.

I replaced the alternator that evening after work (after recharging the batt again so I could get to work and back). Tested it with the voltmeter... no good. Only getting 11 something after starting the engine. Tried another new alt the next day after work, figuring the first new one was bad. Again, no luck. Tried a THIRD new one, and again no good. Each night I'm recharging the batt with the charger.

Next night, got stranded again, this time about 1.5 hrs from home the opposite direction while delivering something for my work (I should have turned it down as I knew I still had an issue with the charging system. Headlights start dimming on the highway, so I swing up the offramp, and then they cut out entirely. Swing into a gas station parking lot in a fairly bad part of the city I was passing through, just as the engine cuts out. This time, got picked up as I was close to my grandparents (thank God). Took the batt with me, charged it overnight at their house (I was keeping the charger in my trunk at this point until I could figure this thing out, as this was my only vehicle and I commuted 60 miles/day round trip to work), and went back the next morning to the gas station parking lot where I left the car. This time, my father who also lived fairly nearby was able to meet me there to try and help me figure out the problem. We poked around and finally found a huge fuse for the alt. (100 amp IIRC) and one of its wires was not bolted in place in the fuse block! It looked like it had never been connected from the factory... the nut was down tight, but the wire was not even in place! It had signs of arcing as it was burnt some, as if that was how it had been passing current for at least a year since I had owned the car. I connected the wire and presto, 14.5 volts w/ the engine running. Got to work, but then found that the new battery I had installed just a year before no longer would hold a charge and needed replacing, from all the draining and recharging. Don't ever want to go through all that again, not to mention swapping the alt in and out three times.

I guess the moral of the story is... besides thinking about a new alt, check for loose wiring, too... and try to get it resolved before continuing to commute and make trips for work, at night time, far away from home. And, be thankful for a great mom, caring grand parents, and have your dad (who lives 1.25 hrs away ) take a look at the problem, too, because he'll probably catch what you missed.

That was actually fun to type all that, and sure is funny thinking back on it. Hope everyone enjoys and learns from my mistakes ... get your charging system fixed before you keep driving.

 

I better get on it then... the batteries aren't even 9 months old!!
CedricR.

 

Yeah, those kind of memories are fun to recall..... but have you noticed that when those things happen when you get older.... they aren't much fun at all?

BTW... while I'm out spending money that I don't have..... is the stock/replacement alternator "adequate"? Are there any bigger/better alts available?

CedricR.

 

There are bigger units available.

I have read that the larger amperage units need to spin up to higher RPMs to reach their advantage, so they may actually put out less at idle and lower rpms than the stock size.

One aftermarket I know of is the Mean Green for around $320. Probably only need to get a bigger unit like this one if you run a lot of electronics or emergency lighting on your truck.

A good source for a stock replacement unit if you end up needing one is the Ebay store for dbelectrical.com for around $150, and it's a 170 amp unit. You have to go to their ebay store and search for "7.3" to get to it.

 

They had a 200 amp unit for $189.00. That price sounds ok for that big of a unit. However, I'll see what the local parts store says. Maybe that'll work out; no shipping, available today, etc.

Thanks for all the help! CedricR.

 

Cedman, if you put in a new alternator and the light still goes on and off like mine did with a new alternator look for a short in the wiring harness to the alternator, mine had a wire in the harness rubbed bare and grounding out.

Walt

 

Had a few minutes this morning so I put the digital meter on the batteries... 12.78v on one and 12.62v on the other with the engine off and cold.

Started her up and lo and behold.... 12.16v on one and 12.17v on the other!

I hear an alternator calling my name.
CedricR.

 

Yep, I think so too, Cedric. Is the battery light still illuminated in the dash?

 

Got a stock alt from Advance for 190.00 out the door. Took me 15 minutes to install. (would have taken a competent tech 5 minutes). Readings before startup on a hot engine were 12.34v and 12.34v. After startup readings were 14.36v and 14.45v.

Peace of mind, peace of mind. What kind of a price can you put on that?

Thanks again everyone who responded.
CedricR.

 

Nope, it's out... probably a burnt out bulb!!! HA!
CedricR.