Whalefish Posted February 21, 2014 Report Share Posted February 21, 2014 Howdy folks. I've got an 84 720 4x4 that has an electical or alternator issue I think. The other day the battery light popped on and the truck lurched a bit. The voltage dropped to 12, and the battery light went on. At idle the truck died, but with some revving the light would click back off and the voltage bumped back up to 14ish. This happens a few times over 2 days, and now will not stop. I checked the battery, all good. Wires leading to the alternator seem to read 12v. I tried running the truck with the alternator plug disconnected and it ran fine, albeit at 12v. While running I reconnected the plug and immediately the truck died. Any ideas? Is there a short somewhere? The alternator is only a few months old, is be surprised if it's that. Thanks in advance! Matt 1 Quote Link to comment
datzenmike Posted February 22, 2014 Report Share Posted February 22, 2014 12 volts is a charged battery. With engine running it should be 13.8 to 14.5 ish. With headlights and heater on the same when revved and just slightly lower at idle Rebuilt alternators are often a 50% fail rate right out of the box. A new Nissan one is close to $300 so a $60 one from Pep Boys is worth exactly that. Any chance you have the original one??? It probably only needed new brushes. If not take it back and have them check it on their machine. 1 Quote Link to comment
Whalefish Posted February 24, 2014 Author Report Share Posted February 24, 2014 Thanks for the response Mike. This alternator is from oreillys, not sure about the fate of the original alternator. An interesting development with the problem today. The truck ran fine for most of the day, alternator charging at 14v. Towards the end of the day the battery light started flickering and the voltmeter dropped to 12 at the same time. My passenger noticed a buzzing sound coming from a small black box with a bunch of wires coming in and out of it. It was like an electrical short kind of buzzing, and coincided exactly with the battery light coming on, the voltage dropping, and the engine lurching, and if at low rpm, the engine stalling. If I revved the engine in neutral, the light would go off... So what the heck is going on? I'm guessing an electrical short, but there were no obvious frayed wires when I looked...I'll look closer tomorrow. Any ideas? Matt 1 Quote Link to comment
Whalefish Posted February 24, 2014 Author Report Share Posted February 24, 2014 And just for reference, this black box is located just below the glove box behind the plastic panel. 1 Quote Link to comment
MikeRL411 Posted February 24, 2014 Report Share Posted February 24, 2014 12 volts is a charged battery. With engine running it should be 13.8 to 14.5 ish. With headlights and heater on the same when revved and just slightly lower at idle Rebuilt alternators are often a 50% fail rate right out of the box. A new Nissan one is close to $300 so a $60 one from Pep Boys is worth exactly that. Any chance you have the original one??? It probably only needed new brushes. If not take it back and have them check it on their machine. "Standard" part number JX-99 alternator brushes. 1 Quote Link to comment
banzai510(hainz) Posted February 24, 2014 Report Share Posted February 24, 2014 You could alwasy take it to Napa and get it load cked. But seems your is after a little driveing 1 Quote Link to comment
datzenmike Posted February 24, 2014 Report Share Posted February 24, 2014 Thanks for the response Mike. This alternator is from oreillys, not sure about the fate of the original alternator. An interesting development with the problem today. The truck ran fine for most of the day, alternator charging at 14v. Towards the end of the day the battery light started flickering and the voltmeter dropped to 12 at the same time. My passenger noticed a buzzing sound coming from a small black box with a bunch of wires coming in and out of it. So what the heck is going on? I'm guessing an electrical short, but there were no obvious frayed wires when I looked...I'll look closer tomorrow. Any ideas? Matt And just for reference, this black box is located just below the glove box behind the plastic panel. . That is very common with 720s that have no output from their alternators. It's the choke heater relay. It needs 14 volts from the charging battery and charge from the alternator in order to stay ON. When the alternator fails there is only 12 volts from the battery and the relay relaxes to the OFF position. When the alternator is bad the relay buzzes on off like a flickering light. It's not the relay's fault but a charging problem, or what the relay thinks is a charging problem. You will find that without the choke heater relay on the choke may not fully come off when warmed up and the fast idle may be engaged causing very poor mileage. Attached to the positive battery cable near the battery post are the 3 fusible links. Two Green and a Black. (usually) The connection between the alt. and the battery is through the Black wire but inspect them all. These act like fuses but designed to melt inside the insulation without catching fire. Thus they may 'look' fine but be damaged inside. They may also be obviously melted. Check the connector contacts are clean and making good contact also. Check the alternator plastic two wire plug. If this doesn't help them have the alt. tested, especially under a load condition. 1 Quote Link to comment
dr.feltersnatch Posted February 24, 2014 Report Share Posted February 24, 2014 Sounds like voltage regulator is failing, Not sure what kind of warranty you got with it but I would take it out and take it back to have it tested and replaced. 1 Quote Link to comment
Whalefish Posted February 25, 2014 Author Report Share Posted February 25, 2014 Thanks for all the responses. I'm chasing down the receipt for the alternator, but in the meantime, I checked the voltages leading to the alternator. All wires we're reading 12.2. volts. The choke relay problem makes sense, I've noticed that the idle has been high since this issue started last week. I'm going to have the alternator checked at oreillys shortly. 1 Quote Link to comment
TasoZ24 Posted January 12, 2015 Report Share Posted January 12, 2015 have you replaced relay? did it help? Im having charging issues as well. would a burnt indicator prohibit the alternator from charging? 1 Quote Link to comment
datzenmike Posted January 12, 2015 Report Share Posted January 12, 2015 The relay probably isn't the problem as it needs a charging alternator in order to work. If you suspect you have a charging issue then this is likely the problem with your relay too. Yes, a burned out charge indicator lamp in the dash would prevent the alternator working. The test for the lamp is turn the ignition switch on, don't start. The red charge lamp should light. Start and it should go out if the alternator is charging. Get a cheap meter or borrow one and check across the battery posts. you should read about 12 volts engine off and just over 14 while running. 1 Quote Link to comment
TasoZ24 Posted January 13, 2015 Report Share Posted January 13, 2015 Ive replaced the bulb and still no light or charge. Im getting a steady 12.2 at battery and 11.5 at alt terminal at idle and goes over 15 when revving. Only 2.34 amps idle 1 Quote Link to comment
TasoZ24 Posted January 13, 2015 Report Share Posted January 13, 2015 Second "new" alt, new battery. Voltage regulator failing at part shop. 1983 2wd 720 with a major wire fail. Getting power everywhere it needs to be with no resistance. Back or cluster is pretty bad, any to bypass this light or any to gert a more modern cluster? 1 Quote Link to comment
Charlie69 Posted January 13, 2015 Report Share Posted January 13, 2015 Please post a picture of the "Back or cluster is pretty bad". To vague of statement. There is a removable pigtail that plugs into the main harness and the plugs into the back of the instrument cluster. This harness has 2 plugs that connect to the main harness above the the fuse block. Quote Link to comment
TasoZ24 Posted January 14, 2015 Report Share Posted January 14, 2015 Got a pick of when I cleaned it up. New here, will post when I figure it out. The internal regulator keeps failing, have dash pulled now trying to follow wires. Trying to get light come on then ill worry about the rest. Quote Link to comment
TasoZ24 Posted January 14, 2015 Report Share Posted January 14, 2015 Getting low readings at the cluster to harness connections. How does one go about posting pics? Quote Link to comment
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