JoeR Posted January 8, 2012 Report Share Posted January 8, 2012 I was driving along the freeway last night and noticed that the battery charge light was glowing very dimly. My truck is running fine otherwise. I checked the owners manual and it says that if the light is glowing and everything else is functioning properly, the load on the alternator is higher than normal and everything should be fine. I had to run a few errands and the truck started up with no problems so the battery seems OK. If it makes any difference, the alternator and battery are both about 6 months old. Any thoughts? Thanks. Quote Link to comment
DailyDato Posted January 8, 2012 Report Share Posted January 8, 2012 What truck? What year? what engine? granted ur stats say 85 720, but, you dont state anything in ur post Quote Link to comment
philcas1987 Posted January 8, 2012 Report Share Posted January 8, 2012 buy a multimeter? Quote Link to comment
ariascarlos1990 Posted January 8, 2012 Report Share Posted January 8, 2012 Get one of these! http://www.amazon.co...r/dp/B000EVWDU0 Quote Link to comment
bananahamuck Posted January 8, 2012 Report Share Posted January 8, 2012 For my wife.. Quote Link to comment
JoeR Posted January 8, 2012 Author Report Share Posted January 8, 2012 I have an 85 720 with a 2.4 Z24. I don't have a cigarette lighter in the truck so that meter would not work. I do have access to a multimeter so I will check the battery asap. Quote Link to comment
Z-train Posted January 8, 2012 Report Share Posted January 8, 2012 Check the battery and then the terminal on the back of the alternator-the two should jive. Quote Link to comment
Skib Posted January 8, 2012 Report Share Posted January 8, 2012 this is why I always install a volt gauge in every car I own, I always know what its doing. Quote Link to comment
Roger d Posted January 10, 2012 Report Share Posted January 10, 2012 Not sure about your issue, but my battery light glows brighter as you turn on more assesories. I assumed the alternator wasn't keeping up, so I put the multi-meter on it and to my suprise, it is charging 15.5 volts! I'm sure it'll cook the battery as it is bubbly. Any ideas out there? Thanks Roger 1 Quote Link to comment
Drazz100 Posted January 10, 2012 Report Share Posted January 10, 2012 Not sure about your issue, but my battery light glows brighter as you turn on more assesories. I assumed the alternator wasn't keeping up, so I put the multi-meter on it and to my suprise, it is charging 15.5 volts! I'm sure it'll cook the battery as it is bubbly. Any ideas out there? Thanks Roger Mine is the same.my battery light is on and will flicker according to how i rev the engine.Also showing about 16V on the gauge. Idles at about 14V but when I start driving it,it goes up mto 16 or so Quote Link to comment
DanielC Posted January 10, 2012 Report Share Posted January 10, 2012 Some charge lights on cars are wires so they have 12 volts from the battery applied to one side of the light, and when the alternator starts to charge, it applies alternator voltage to the other side of the light. When you turn the key on, the alternator is not turning, or making electricity, and the charge light is on, brightly. After the engine starts, the alternator makes voltage, and that opposes the battery voltage and the light turns off. If the alternator puts out significantly more voltage that the battery, the light could glow dimly. Check the charging voltage with a good voltmeter. 13.5 to 14.5 is OK, engine running about 2000 RPM. If the voltage is higher than that, the first thing I would do is to clean all the grounds from the battery to the alternator. Clean all the connections in the positive side of the charging circuit, also, and THAT INCLUDES THE BATTERY TERMINALS! An external Datsun Regulator will have a slightly higher voltage, when it is cold, the regulator is temperature compensated. I do not know when Datsun switched over to internal regulated alternators. Quote Link to comment
ggzilla Posted January 10, 2012 Report Share Posted January 10, 2012 That's how Datsun charge lights are wired too. They changed to Internal Regulator in 1979 Check the voltage. If it's between 13.5 - 15 then all is good. My 1981 manual says if over 15.5 replace the regulator (get a different alternator). I found in my case that the dim charge light eventually got worse. After about six months it no longer charged. 1981 Factory Service Manual says: Engine speed 1,500 rpm, Lighting switch ON: Dim charge light -> Engine idling (Measure the voltage across B and L terminals:* more than 0.5v -> fault alternator (except regulator) * Less than 0.5v -> OK Engine speed 1,500 rpm, Lighting switch OFF: * More than 15.5v -> replace regulator * 13v to 15v -> Engine idling, Lighting switch ON: * Charge light on -> faulty alternator (except regulator) * Charge light off: OK Quote Link to comment
datsunaholic Posted January 10, 2012 Report Share Posted January 10, 2012 If the light gets brighter with RPM, and the voltage is over 15 - 15.5 then the regulator is fried. Since the regulator is inside the alternator on the 720s, that means you either need a new alternator or would have to replace the internal regulator (doable, I've done it, but might as well change brushes and inspect bearings at that point). I had one go bad on the freeway- jumped to nearly 20V. I quickly turned EVERYTHING on (heater, headlights) and it fell to 14.5V, but turn off accessories and it badly wanted to overcharge. Fortunately I make a habit of checking gauges and caught it before the battery exploded. If it's a dim glow, but the voltage is in the normal range then it's at overload. Since the 720 alternator can power EVERYTHING in the truck simultaneously (unless you have massive baja lights, a huge amplifier, or some other massive electrical load), the light shouldn't glow. If the voltage is charging but low (above 12.3V but below 13.7v) then the alternator is getting tired, usually brushes but could be something else. 1 Quote Link to comment
86 720 Posted January 12, 2012 Report Share Posted January 12, 2012 Had that same problem when I first bought my 720. The light would stay ever so dim, was only really able to see it at night, and at first I thought there was some light creeping in from the cluster. Turned out to be a bad alternator, and I had JUST replaced it with a "new" one. I took it out, had Autzone test it three times, and it passed "ok". Had them test it one last time, and it failed. Got a new one, had them test it 6 times and haven't had any problems since. Now I always have Autozone run a test at least 6 times, even on "new" replacement parts. 1 Quote Link to comment
JoeR Posted January 13, 2012 Author Report Share Posted January 13, 2012 All is good, I found a short in the fusable link I installed a few month back. Replaced it and all is well. Quote Link to comment
ggzilla Posted January 13, 2012 Report Share Posted January 13, 2012 Glad to hear it is fixed. Happy driving! Quote Link to comment
lego126 Posted July 30, 2014 Report Share Posted July 30, 2014 I know this is an old post, but my batt. Light is slightly on as well. I've had it tested several times, all good. And it the same alt that's been in it since I acquired the truck several years back. I would think if the alt would have have gone by now if it were indeed a tired alt. I'm sure there a wire somewhere. I just hope its not too hard to find. Quote Link to comment
datzenmike Posted July 30, 2014 Report Share Posted July 30, 2014 Get a volt meter and check across the battery when running. Should be just above 14 volts. If less it could be charging, but at a reduced rate. Quote Link to comment
Charlie69 Posted July 30, 2014 Report Share Posted July 30, 2014 My 720 is doing it and I replaced alternator was fine for a few days and started doing it again. My battery know tests bad so I will change it out on Saturday. I will also have the alternator tested. Quote Link to comment
bryant2482 Posted July 31, 2014 Report Share Posted July 31, 2014 sounds like the alternator is going out. mine had the exact same issue. the diodes were going bad. the alternator is putting out the correct voltage and amps and keeps the batt. light off, otherwise if not (like in your situation) then the light comes one. i know it sounds strange but thats just how nissan made these Quote Link to comment
Charlie69 Posted August 2, 2014 Report Share Posted August 2, 2014 My rebuilt alternator died only putting out 4 Volts.. I have one on order through Napa this time. Should have it tomorrow. Quote Link to comment
Charlie69 Posted August 3, 2014 Report Share Posted August 3, 2014 Replaced alternator again and no light. All is good. Quote Link to comment
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.